diff --git a/Cargo.lock b/Cargo.lock
index c67c036bd7..01c5b5e10f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2042,7 +2042,7 @@ dependencies = [
 
 [[package]]
 name = "weedle2"
-version = "4.0.0"
+version = "4.0.1"
 dependencies = [
  "fs-err",
  "nom",
diff --git a/fixtures/keywords/kotlin/src/keywords.udl b/fixtures/keywords/kotlin/src/keywords.udl
index 6cdd7a6f07..f9a6c76597 100644
--- a/fixtures/keywords/kotlin/src/keywords.udl
+++ b/fixtures/keywords/kotlin/src/keywords.udl
@@ -7,7 +7,8 @@ interface break {
     void object(u8? class);
 };
 
-callback interface continue {
+[Trait]
+interface continue {
     return return(return v);
     continue? continue();
     record<u8, break> break(break? v);
diff --git a/fixtures/keywords/kotlin/src/lib.rs b/fixtures/keywords/kotlin/src/lib.rs
index d5c63ab780..bfdd8bd117 100644
--- a/fixtures/keywords/kotlin/src/lib.rs
+++ b/fixtures/keywords/kotlin/src/lib.rs
@@ -15,9 +15,9 @@ impl r#break {
 }
 
 #[allow(non_camel_case_types)]
-trait r#continue {
+trait r#continue: Send + Sync {
     fn r#return(&self, v: r#return) -> r#return;
-    fn r#continue(&self) -> Option<Box<dyn r#continue>>;
+    fn r#continue(&self) -> Option<Arc<dyn r#continue>>;
     fn r#break(&self, _v: Option<Arc<r#break>>) -> HashMap<u8, Arc<r#break>>;
     fn r#while(&self, _v: Vec<r#while>) -> r#while;
     fn class(&self, _v: HashMap<u8, Vec<class>>) -> Option<HashMap<u8, Vec<class>>>;
diff --git a/fixtures/keywords/rust/src/keywords.udl b/fixtures/keywords/rust/src/keywords.udl
index 1edc1cdb6b..a66335953a 100644
--- a/fixtures/keywords/rust/src/keywords.udl
+++ b/fixtures/keywords/rust/src/keywords.udl
@@ -13,7 +13,8 @@ interface break {
     void async(u8? yield);
 };
 
-callback interface continue {
+[Trait]
+interface continue {
     return return(return v);
     continue? continue();
     record<u8, break> break(break? v);
diff --git a/fixtures/keywords/rust/src/lib.rs b/fixtures/keywords/rust/src/lib.rs
index 0b93557307..b3a7610350 100644
--- a/fixtures/keywords/rust/src/lib.rs
+++ b/fixtures/keywords/rust/src/lib.rs
@@ -16,15 +16,15 @@ impl r#break {
     pub fn r#break(&self, v: HashMap<u8, Arc<r#break>>) -> Option<HashMap<u8, Arc<r#break>>> {
         Some(v)
     }
-    fn r#continue(&self, _v: Vec<Box<dyn r#continue>>) {}
+    fn r#continue(&self, _v: Vec<Arc<dyn r#continue>>) {}
     pub fn r#yield(&self, _async: u8) {}
     pub fn r#async(&self, _yield: Option<u8>) {}
 }
 
 #[allow(non_camel_case_types)]
-pub trait r#continue {
+pub trait r#continue: Send + Sync {
     fn r#return(&self, v: r#return) -> r#return;
-    fn r#continue(&self) -> Option<Box<dyn r#continue>>;
+    fn r#continue(&self) -> Option<Arc<dyn r#continue>>;
     fn r#break(&self, _v: Option<Arc<r#break>>) -> HashMap<u8, Arc<r#break>>;
     fn r#while(&self, _v: Vec<r#while>) -> r#while;
     fn r#yield(&self, _v: HashMap<u8, Vec<r#yield>>) -> Option<HashMap<u8, Vec<r#yield>>>;
diff --git a/fixtures/proc-macro/tests/bindings/test_proc_macro.swift b/fixtures/proc-macro/tests/bindings/test_proc_macro.swift
index f8a1618f15..bd9fef7f3f 100644
--- a/fixtures/proc-macro/tests/bindings/test_proc_macro.swift
+++ b/fixtures/proc-macro/tests/bindings/test_proc_macro.swift
@@ -84,8 +84,7 @@ class SwiftTestCallbackInterface : TestCallbackInterface {
     }
 
     func callbackHandler(h: Object) -> UInt32 {
-        var v = h.takeError(e: BasicError.InvalidInput)
-        return v
+        return h.takeError(e: BasicError.InvalidInput)
     }
 
     func getOtherCallbackInterface() -> OtherCallbackInterface {
diff --git a/uniffi_bindgen/src/bindings/kotlin/gen_kotlin/mod.rs b/uniffi_bindgen/src/bindings/kotlin/gen_kotlin/mod.rs
index 74e0b2eef4..86c08aae6c 100644
--- a/uniffi_bindgen/src/bindings/kotlin/gen_kotlin/mod.rs
+++ b/uniffi_bindgen/src/bindings/kotlin/gen_kotlin/mod.rs
@@ -310,7 +310,12 @@ impl KotlinCodeOracle {
 
     /// Get the idiomatic Kotlin rendering of a variable name.
     fn var_name(&self, nm: &str) -> String {
-        format!("`{}`", nm.to_string().to_lower_camel_case())
+        format!("`{}`", self.var_name_raw(nm))
+    }
+
+    /// `var_name` without the backticks.  Useful for using in `@Structure.FieldOrder`.
+    pub fn var_name_raw(&self, nm: &str) -> String {
+        nm.to_string().to_lower_camel_case()
     }
 
     /// Get the idiomatic Kotlin rendering of an individual enum variant.
@@ -318,11 +323,16 @@ impl KotlinCodeOracle {
         nm.to_string().to_shouty_snake_case()
     }
 
-    /// Get the idiomatic Python rendering of an FFI callback function
+    /// Get the idiomatic Kotlin rendering of an FFI callback function name
     fn ffi_callback_name(&self, nm: &str) -> String {
         format!("Uniffi{}", nm.to_upper_camel_case())
     }
 
+    /// Get the idiomatic Kotlin rendering of an FFI struct name
+    fn ffi_struct_name(&self, nm: &str) -> String {
+        format!("Uniffi{}", nm.to_upper_camel_case())
+    }
+
     fn ffi_type_label_by_value(&self, ffi_type: &FfiType) -> String {
         match ffi_type {
             FfiType::RustBuffer(_) => format!("{}.ByValue", self.ffi_type_label(ffi_type)),
@@ -330,6 +340,25 @@ impl KotlinCodeOracle {
         }
     }
 
+    fn ffi_type_label_by_reference(&self, ffi_type: &FfiType) -> String {
+        match ffi_type {
+            FfiType::Int8
+            | FfiType::UInt8
+            | FfiType::Int16
+            | FfiType::UInt16
+            | FfiType::Int32
+            | FfiType::UInt32
+            | FfiType::Int64
+            | FfiType::UInt64
+            | FfiType::Float32
+            | FfiType::Float64 => format!("{}ByReference", self.ffi_type_label(ffi_type)),
+            FfiType::RustArcPtr(_) => "PointerByReference".to_owned(),
+            // JNA structs default to ByReference
+            FfiType::RustBuffer(_) | FfiType::Struct(_) => self.ffi_type_label(ffi_type),
+            _ => panic!("{ffi_type:?} by reference is not implemented"),
+        }
+    }
+
     fn ffi_type_label(&self, ffi_type: &FfiType) -> String {
         match ffi_type {
             // Note that unsigned integers in Kotlin are currently experimental, but java.nio.ByteBuffer does not
@@ -347,8 +376,9 @@ impl KotlinCodeOracle {
             }
             FfiType::ForeignBytes => "ForeignBytes.ByValue".to_string(),
             FfiType::Callback(name) => self.ffi_callback_name(name),
-            FfiType::ForeignCallback => "ForeignCallback".to_string(),
-            FfiType::RustFutureHandle => "Pointer".to_string(),
+            FfiType::Struct(name) => self.ffi_struct_name(name),
+            FfiType::Reference(inner) => self.ffi_type_label_by_reference(inner),
+            FfiType::VoidPointer | FfiType::RustFutureHandle => "Pointer".to_string(),
             FfiType::RustFutureContinuationData => "USize".to_string(),
         }
     }
@@ -500,6 +530,11 @@ mod filters {
         Ok(KotlinCodeOracle.var_name(nm))
     }
 
+    /// Get the idiomatic Kotlin rendering of a variable name.
+    pub fn var_name_raw(nm: &str) -> Result<String, askama::Error> {
+        Ok(KotlinCodeOracle.var_name_raw(nm))
+    }
+
     /// Get a String representing the name used for an individual enum variant.
     pub fn variant_name(v: &Variant) -> Result<String, askama::Error> {
         Ok(KotlinCodeOracle.enum_variant_name(v.name()))
@@ -515,6 +550,11 @@ mod filters {
         Ok(KotlinCodeOracle.ffi_callback_name(nm))
     }
 
+    /// Get the idiomatic Kotlin rendering of an FFI struct name
+    pub fn ffi_struct_name(nm: &str) -> Result<String, askama::Error> {
+        Ok(KotlinCodeOracle.ffi_struct_name(nm))
+    }
+
     pub fn object_names(
         obj: &Object,
         ci: &ComponentInterface,
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/Async.kt b/uniffi_bindgen/src/bindings/kotlin/templates/Async.kt
index f433fd80e6..141a9681de 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/Async.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/Async.kt
@@ -15,7 +15,7 @@ internal object uniffiRustFutureContinuationCallback: UniffiRustFutureContinuati
 internal suspend fun<T, F, E: Exception> uniffiRustCallAsync(
     rustFuture: Pointer,
     pollFunc: (Pointer, UniffiRustFutureContinuationCallback, USize) -> Unit,
-    completeFunc: (Pointer, UnifiRustCallStatus) -> F,
+    completeFunc: (Pointer, UniffiRustCallStatus) -> F,
     freeFunc: (Pointer) -> Unit,
     liftFunc: (F) -> T,
     errorHandler: UniffiRustCallStatusErrorHandler<E>
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceImpl.kt b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceImpl.kt
index 77794cb045..80bc4d3399 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceImpl.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceImpl.kt
@@ -1,107 +1,70 @@
 {% if self.include_once_check("CallbackInterfaceRuntime.kt") %}{% include "CallbackInterfaceRuntime.kt" %}{% endif %}
 
-// Implement the foreign callback handler for {{ interface_name }}
-internal class {{ callback_handler_class }} : ForeignCallback {
-    @Suppress("TooGenericExceptionCaught")
-    override fun invoke(handle: UniffiHandle, method: Int, argsData: Pointer, argsLen: Int, outBuf: RustBufferByReference): Int {
-        val cb = {{ ffi_converter_name }}.handleMap.get(handle)
-        return when (method) {
-            IDX_CALLBACK_FREE -> {
-                {{ ffi_converter_name }}.handleMap.remove(handle)
+{%- let trait_impl=format!("uniffiCallbackInterface{}", name) %}
 
-                // Successful return
-                // See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-                UNIFFI_CALLBACK_SUCCESS
-            }
-            {% for meth in methods.iter() -%}
-            {% let method_name = format!("invoke_{}", meth.name())|fn_name -%}
-            {{ loop.index }} -> {
-                // Call the method, write to outBuf and return a status code
-                // See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs` for info
-                try {
-                    this.{{ method_name }}(cb, argsData, argsLen, outBuf)
-                } catch (e: Throwable) {
-                    // Unexpected error
-                    try {
-                        // Try to serialize the error into a string
-                        outBuf.setValue({{ Type::String.borrow()|ffi_converter_name }}.lower(e.toString()))
-                    } catch (e: Throwable) {
-                        // If that fails, then it's time to give up and just return
-                    }
-                    UNIFFI_CALLBACK_UNEXPECTED_ERROR
-                }
-            }
-            {% endfor %}
-            else -> {
-                // An unexpected error happened.
-                // See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-                try {
-                    // Try to serialize the error into a string
-                    outBuf.setValue({{ Type::String.borrow()|ffi_converter_name }}.lower("Invalid Callback index"))
-                } catch (e: Throwable) {
-                    // If that fails, then it's time to give up and just return
-                }
-                UNIFFI_CALLBACK_UNEXPECTED_ERROR
+// Put the implementation in an object so we don't pollute the top-level namespace
+internal object {{ trait_impl }} {
+    {%- for (ffi_callback, meth) in vtable_methods.iter() %}
+    internal object {{ meth.name()|var_name }}: {{ ffi_callback.name()|ffi_callback_name }} {
+        override fun callback(
+            {%- for arg in ffi_callback.arguments() -%}
+            {{ arg.name().borrow()|var_name }}: {{ arg.type_().borrow()|ffi_type_name_by_value }},
+            {%- endfor -%}
+            {%- if ffi_callback.has_rust_call_status_arg() -%}
+            uniffiCallStatus: UniffiRustCallStatus,
+            {%- endif -%}
+        )
+        {%- match ffi_callback.return_type() %}
+        {%- when Some(return_type) %}: {{ return_type|ffi_type_name_by_value }},
+        {%- when None %}
+        {%- endmatch %} {
+            val uniffiObj = {{ ffi_converter_name }}.handleMap.get(uniffiHandle)
+            val makeCall = { ->
+                uniffiObj.{{ meth.name()|fn_name() }}(
+                    {%- for arg in meth.arguments() %}
+                    {{ arg|lift_fn }}({{ arg.name()|var_name }}),
+                    {%- endfor %}
+                )
             }
-        }
-    }
 
-    {% for meth in methods.iter() -%}
-    {% let method_name = format!("invoke_{}", meth.name())|fn_name %}
-    @Suppress("UNUSED_PARAMETER")
-    private fun {{ method_name }}(kotlinCallbackInterface: {{ interface_name }}, argsData: Pointer, argsLen: Int, outBuf: RustBufferByReference): Int {
-        {%- if meth.arguments().len() > 0 %}
-        val argsBuf = argsData.getByteBuffer(0, argsLen.toLong()).also {
-            it.order(ByteOrder.BIG_ENDIAN)
-        }
-        {%- endif %}
+            {%- match meth.return_type() %}
+            {%- when Some(return_type) %}
+            val writeReturn = { value: {{ return_type|type_name(ci) }} -> uniffiOutReturn.setValue({{ return_type|lower_fn }}(value)) }
+            {%- when None %}
+            val writeReturn = { _: Unit -> Unit }
+            {%- endmatch %}
 
-        {%- match meth.return_type() %}
-        {%- when Some with (return_type) %}
-        fun makeCall() : Int {
-            val returnValue = kotlinCallbackInterface.{{ meth.name()|fn_name }}(
-                {%- for arg in meth.arguments() %}
-                {{ arg|read_fn }}(argsBuf)
-                {% if !loop.last %}, {% endif %}
-                {%- endfor %}
-            )
-            outBuf.setValue({{ return_type|ffi_converter_name }}.lowerIntoRustBuffer(returnValue))
-            return UNIFFI_CALLBACK_SUCCESS
-        }
-        {%- when None %}
-        fun makeCall() : Int {
-            kotlinCallbackInterface.{{ meth.name()|fn_name }}(
-                {%- for arg in meth.arguments() %}
-                {{ arg|read_fn }}(argsBuf)
-                {%- if !loop.last %}, {% endif %}
-                {%- endfor %}
+            {%- match meth.throws_type() %}
+            {%- when None %}
+            uniffiTraitInterfaceCall(uniffiCallStatus, makeCall, writeReturn)
+            {%- when Some(error_type) %}
+            uniffiTraitInterfaceCallWithError(
+                uniffiCallStatus,
+                makeCall,
+                writeReturn,
+                { e: {{error_type|type_name(ci) }} -> {{ error_type|lower_fn }}(e) }
             )
-            return UNIFFI_CALLBACK_SUCCESS
+            {%- endmatch %}
         }
-        {%- endmatch %}
+    }
+    {%- endfor %}
 
-        {%- match meth.throws_type() %}
-        {%- when None %}
-        fun makeCallAndHandleError() : Int = makeCall()
-        {%- when Some(error_type) %}
-        fun makeCallAndHandleError()  : Int = try {
-            makeCall()
-        } catch (e: {{ error_type|type_name(ci) }}) {
-            // Expected error, serialize it into outBuf
-            outBuf.setValue({{ error_type|ffi_converter_name }}.lowerIntoRustBuffer(e))
-            UNIFFI_CALLBACK_ERROR
+    internal object uniffiFree: {{ "CallbackInterfaceFree"|ffi_callback_name }} {
+        override fun callback(handle: Long) {
+            {{ ffi_converter_name }}.handleMap.remove(handle)
         }
-        {%- endmatch %}
-
-        return makeCallAndHandleError()
     }
-    {% endfor %}
+
+    internal var vtable = {{ vtable|ffi_type_name_by_value }}(
+        {%- for (ffi_callback, meth) in vtable_methods.iter() %}
+        {{ meth.name()|var_name() }},
+        {%- endfor %}
+        uniffiFree
+    )
 
     // Registers the foreign callback with the Rust side.
     // This method is generated for each callback interface.
     internal fun register(lib: UniffiLib) {
-        lib.{{ ffi_init_callback.name() }}(this)
+        lib.{{ ffi_init_callback.name() }}(vtable)
     }
 }
-
-internal val {{ callback_handler_obj }} = {{ callback_handler_class }}()
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceRuntime.kt b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceRuntime.kt
index e1b25f0e26..e7b7dc4725 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceRuntime.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceRuntime.kt
@@ -32,10 +32,6 @@ internal class ConcurrentHandleMap<T>(
         }
 }
 
-interface ForeignCallback : com.sun.jna.Callback {
-    public fun invoke(handle: UniffiHandle, method: Int, argsData: Pointer, argsLen: Int, outBuf: RustBufferByReference): Int
-}
-
 // Magic number for the Rust proxy to call using the same mechanism as every other method,
 // to free the callback once it's dropped by Rust.
 internal const val IDX_CALLBACK_FREE = 0
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceTemplate.kt b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceTemplate.kt
index 9f104118c7..5285cbc4ab 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceTemplate.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/CallbackInterfaceTemplate.kt
@@ -1,10 +1,10 @@
 {%- let cbi = ci|get_callback_interface_definition(name) %}
-{%- let callback_handler_class = format!("UniffiCallbackInterface{}", name) %}
-{%- let callback_handler_obj = format!("uniffiCallbackInterface{}", name) %}
 {%- let ffi_init_callback = cbi.ffi_init_callback() %}
 {%- let interface_name = cbi|type_name(ci) %}
-{%- let methods = cbi.methods() %}
 {%- let interface_docstring = cbi.docstring() %}
+{%- let methods = cbi.methods() %}
+{%- let vtable = cbi.vtable() %}
+{%- let vtable_methods = cbi.vtable_methods() %}
 
 {% include "Interface.kt" %}
 {% include "CallbackInterfaceImpl.kt" %}
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/Helpers.kt b/uniffi_bindgen/src/bindings/kotlin/templates/Helpers.kt
index a3a992571c..d82a6a7407 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/Helpers.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/Helpers.kt
@@ -1,6 +1,10 @@
 // A handful of classes and functions to support the generated data structures.
 // This would be a good candidate for isolating in its own ffi-support lib.
-// Error runtime.
+
+internal const val UNIFFI_CALL_SUCCESS = 0.toByte()
+internal const val UNIFFI_CALL_ERROR = 1.toByte()
+internal const val UNIFFI_CALL_UNEXPECTED_ERROR = 2.toByte()
+
 @Structure.FieldOrder("code", "error_buf")
 internal open class UniffiRustCallStatus : Structure() {
     @JvmField var code: Byte = 0
@@ -9,15 +13,15 @@ internal open class UniffiRustCallStatus : Structure() {
     class ByValue: UniffiRustCallStatus(), Structure.ByValue
 
     fun isSuccess(): Boolean {
-        return code == 0.toByte()
+        return code == UNIFFI_CALL_SUCCESS
     }
 
     fun isError(): Boolean {
-        return code == 1.toByte()
+        return code == UNIFFI_CALL_ERROR
     }
 
     fun isPanic(): Boolean {
-        return code == 2.toByte()
+        return code == UNIFFI_CALL_UNEXPECTED_ERROR
     }
 }
 
@@ -118,6 +122,37 @@ public class USize(value: Long = 0) : IntegerType(Native.SIZE_T_SIZE, value, tru
     }
 }
 
+internal inline fun<T> uniffiTraitInterfaceCall(
+    callStatus: UniffiRustCallStatus,
+    makeCall: () -> T,
+    writeReturn: (T) -> Unit,
+) {
+    try {
+        writeReturn(makeCall())
+    } catch(e: Exception) {
+        callStatus.code = UNIFFI_CALL_UNEXPECTED_ERROR
+        callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(e.toString())
+    }
+}
+
+internal inline fun<T, reified E: Throwable> uniffiTraitInterfaceCallWithError(
+    callStatus: UniffiRustCallStatus,
+    makeCall: () -> T,
+    writeReturn: (T) -> Unit,
+    lowerError: (E) -> RustBuffer.ByValue
+) {
+    try {
+        writeReturn(makeCall())
+    } catch(e: Exception) {
+        if (e is E) {
+            callStatus.code = UNIFFI_CALL_ERROR
+            callStatus.error_buf = lowerError(e)
+        } else {
+            callStatus.code = UNIFFI_CALL_UNEXPECTED_ERROR
+            callStatus.error_buf = {{ Type::String.borrow()|lower_fn }}(e.toString())
+        }
+    }
+}
 
 // Map handles to objects
 //
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/NamespaceLibraryTemplate.kt b/uniffi_bindgen/src/bindings/kotlin/templates/NamespaceLibraryTemplate.kt
index 6348c3068f..36ffbfcf88 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/NamespaceLibraryTemplate.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/NamespaceLibraryTemplate.kt
@@ -20,13 +20,25 @@ internal interface {{ callback.name()|ffi_callback_name }} : com.sun.jna.Callbac
         {%- for arg in callback.arguments() -%}
         {{ arg.name().borrow()|var_name }}: {{ arg.type_().borrow()|ffi_type_name_by_value }},
         {%- endfor -%}
+        {%- if callback.has_rust_call_status_arg() -%}
+        uniffiCallStatus: UniffiRustCallStatus,
+        {%- endif -%}
     )
     {%- match callback.return_type() %}
     {%- when Some(return_type) %}: {{ return_type|ffi_type_name_by_value }}
     {%- when None %}
     {%- endmatch %}
 }
+{%- endfor %}
 
+// Define FFI structs
+{%- for ffi_struct in ci.ffi_struct_definitions() %}
+@Structure.FieldOrder({% for field in ffi_struct.fields() %}"{{ field.name()|var_name_raw }}"{% if !loop.last %}, {% endif %}{% endfor %})
+internal class {{ ffi_struct.name()|ffi_struct_name }}(
+    {%- for field in ffi_struct.fields() %}
+    @JvmField internal var {{ field.name()|var_name }}: {{ field.type_().borrow()|ffi_type_name_by_value }},
+    {%- endfor %}
+) : Structure() { }
 {%- endfor %}
 
 // A JNA Library to expose the extern-C FFI definitions.
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/ObjectTemplate.kt b/uniffi_bindgen/src/bindings/kotlin/templates/ObjectTemplate.kt
index e73ff3a959..8492b832c7 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/ObjectTemplate.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/ObjectTemplate.kt
@@ -304,8 +304,8 @@ open class {{ impl_class_name }}: Disposable, AutoCloseable, {{ interface_name }
 }
 
 {%- if obj.has_callback_interface() %}
-{%- let callback_handler_class = format!("UniffiCallbackInterface{}", name) %}
-{%- let callback_handler_obj = format!("uniffiCallbackInterface{}", name) %}
+{%- let vtable = obj.vtable().expect("trait interface should have a vtable") %}
+{%- let vtable_methods = obj.vtable_methods() %}
 {%- let ffi_init_callback = obj.ffi_init_callback() %}
 {% include "CallbackInterfaceImpl.kt" %}
 {%- endif %}
diff --git a/uniffi_bindgen/src/bindings/kotlin/templates/RustBufferTemplate.kt b/uniffi_bindgen/src/bindings/kotlin/templates/RustBufferTemplate.kt
index e914d481a4..9e75870175 100644
--- a/uniffi_bindgen/src/bindings/kotlin/templates/RustBufferTemplate.kt
+++ b/uniffi_bindgen/src/bindings/kotlin/templates/RustBufferTemplate.kt
@@ -11,6 +11,12 @@ open class RustBuffer : Structure() {
     class ByValue: RustBuffer(), Structure.ByValue
     class ByReference: RustBuffer(), Structure.ByReference
 
+   internal fun setValue(other: RustBuffer) {
+        capacity = other.capacity
+        len = other.len
+        data = other.data
+    }
+
     companion object {
         internal fun alloc(size: Int = 0) = uniffiRustCall() { status ->
             UniffiLib.INSTANCE.{{ ci.ffi_rustbuffer_alloc().name() }}(size, status)
diff --git a/uniffi_bindgen/src/bindings/python/gen_python/mod.rs b/uniffi_bindgen/src/bindings/python/gen_python/mod.rs
index 8ea4e658d7..699cf22b2f 100644
--- a/uniffi_bindgen/src/bindings/python/gen_python/mod.rs
+++ b/uniffi_bindgen/src/bindings/python/gen_python/mod.rs
@@ -337,11 +337,18 @@ impl PythonCodeOracle {
         fixup_keyword(nm.to_string().to_shouty_snake_case())
     }
 
-    /// Get the idiomatic Python rendering of an FFI callback function
+    /// Get the idiomatic Python rendering of an FFI callback function name
     fn ffi_callback_name(&self, nm: &str) -> String {
         format!("UNIFFI_{}", nm.to_shouty_snake_case())
     }
 
+    /// Get the idiomatic Python rendering of an FFI struct name
+    fn ffi_struct_name(&self, nm: &str) -> String {
+        // The ctypes docs use both SHOUTY_SNAKE_CASE AND UpperCamelCase for structs. Let's use
+        // UpperCamelCase and reserve shouting for global variables
+        format!("Uniffi{}", nm.to_upper_camel_case())
+    }
+
     fn ffi_type_label(&self, ffi_type: &FfiType) -> String {
         match ffi_type {
             FfiType::Int8 => "ctypes.c_int8".to_string(),
@@ -361,9 +368,10 @@ impl PythonCodeOracle {
             },
             FfiType::ForeignBytes => "_UniffiForeignBytes".to_string(),
             FfiType::Callback(name) => self.ffi_callback_name(name),
-            FfiType::ForeignCallback => "_UNIFFI_FOREIGN_CALLBACK_T".to_string(),
+            FfiType::Struct(name) => self.ffi_struct_name(name),
             // Pointer to an `asyncio.EventLoop` instance
-            FfiType::RustFutureHandle => "ctypes.c_void_p".to_string(),
+            FfiType::Reference(inner) => format!("ctypes.POINTER({})", self.ffi_type_label(inner)),
+            FfiType::VoidPointer | FfiType::RustFutureHandle => "ctypes.c_void_p".to_string(),
             FfiType::RustFutureContinuationData => "ctypes.c_size_t".to_string(),
         }
     }
@@ -513,11 +521,16 @@ pub mod filters {
         Ok(PythonCodeOracle.enum_variant_name(nm))
     }
 
-    /// Get the idiomatic Python rendering of a FFI callback function name
+    /// Get the idiomatic Python rendering of an FFI callback function name
     pub fn ffi_callback_name(nm: &str) -> Result<String, askama::Error> {
         Ok(PythonCodeOracle.ffi_callback_name(nm))
     }
 
+    /// Get the idiomatic Python rendering of an FFI struct name
+    pub fn ffi_struct_name(nm: &str) -> Result<String, askama::Error> {
+        Ok(PythonCodeOracle.ffi_struct_name(nm))
+    }
+
     /// Get the idiomatic Python rendering of an individual enum variant.
     pub fn object_names(obj: &Object) -> Result<(String, String), askama::Error> {
         Ok(PythonCodeOracle.object_names(obj))
diff --git a/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceImpl.py b/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceImpl.py
index 23866a1994..82907e6cd3 100644
--- a/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceImpl.py
+++ b/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceImpl.py
@@ -1,91 +1,62 @@
 {% if self.include_once_check("CallbackInterfaceRuntime.py") %}{% include "CallbackInterfaceRuntime.py" %}{% endif %}
-
-# Declaration and _UniffiConverters for {{ type_name }} Callback Interface
-
-def {{ callback_handler_class }}(handle, method, args_data, args_len, buf_ptr):
-    {% for meth in methods.iter() -%}
-    {% let method_name = format!("invoke_{}", meth.name())|fn_name %}
-    def {{ method_name }}(python_callback, args_stream, buf_ptr):
-        {#- Unpacking args from the _UniffiRustBuffer #}
-        def makeCall():
-            {#- Calling the concrete callback object #}
-            {%- if meth.arguments().len() != 0 -%}
-            return python_callback.{{ meth.name()|fn_name }}(
-                {% for arg in meth.arguments() -%}
-                {{ arg|read_fn }}(args_stream)
-                {%- if !loop.last %}, {% endif %}
-                {% endfor -%}
-            )
-            {%- else %}
-            return python_callback.{{ meth.name()|fn_name }}()
+{%- let trait_impl=format!("UniffiTraitImpl{}", name) %}
+
+# Put all the bits inside a class to keep the top-level namespace clean
+class {{ trait_impl }}:
+    # For each method, generate a callback function to pass to Rust
+    {%- for (ffi_callback, meth) in vtable_methods.iter() %}
+
+    @{{ ffi_callback.name()|ffi_callback_name }}
+    def {{ meth.name()|fn_name }}(
+            {%- for arg in ffi_callback.arguments() %}
+            {{ arg.name()|var_name }},
+            {%- endfor -%}
+            {%- if ffi_callback.has_rust_call_status_arg() %}
+            uniffi_call_status_ptr,
             {%- endif %}
-
-        def makeCallAndHandleReturn():
-            {%- match meth.return_type() %}
-            {%- when Some(return_type) %}
-            rval = makeCall()
-            with _UniffiRustBuffer.alloc_with_builder() as builder:
-                {{ return_type|write_fn }}(rval, builder)
-                buf_ptr[0] = builder.finalize()
-            {%- when None %}
-            makeCall()
-            {%- endmatch %}
-            return _UNIFFI_CALLBACK_SUCCESS
+        ):
+        uniffi_obj = {{ ffi_converter_name }}._handle_map.get(uniffi_handle)
+        def make_call():
+            args = ({% for arg in meth.arguments() %}{{ arg|lift_fn }}({{ arg.name()|var_name }}), {% endfor %})
+            method = uniffi_obj.{{ meth.name()|fn_name }}
+            return method(*args)
+        {%- match meth.return_type() %}
+        {%- when Some(return_type) %}
+        def write_return_value(v):
+            uniffi_out_return[0] = {{ return_type|lower_fn }}(v)
+        {%- when None %}
+        write_return_value = lambda v: None
+        {%- endmatch %}
 
         {%- match meth.throws_type() %}
         {%- when None %}
-        return makeCallAndHandleReturn()
-        {%- when Some(err) %}
-        try:
-            return makeCallAndHandleReturn()
-        except {{ err|type_name }} as e:
-            # Catch errors declared in the UDL file
-            with _UniffiRustBuffer.alloc_with_builder() as builder:
-                {{ err|write_fn }}(e, builder)
-                buf_ptr[0] = builder.finalize()
-            return _UNIFFI_CALLBACK_ERROR
+        _uniffi_trait_interface_call(
+                uniffi_call_status_ptr.contents,
+                make_call,
+                write_return_value,
+        )
+        {%- when Some(error) %}
+        _uniffi_trait_interface_call_with_error(
+                uniffi_call_status_ptr.contents,
+                make_call,
+                write_return_value,
+                {{ error|type_name }},
+                {{ error|lower_fn }},
+        )
         {%- endmatch %}
-
-    {% endfor %}
-
-    cb = {{ ffi_converter_name }}._handle_map.get(handle)
-
-    if method == IDX_CALLBACK_FREE:
-        {{ ffi_converter_name }}._handle_map.remove(handle)
-
-        # Successful return
-        # See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-        return _UNIFFI_CALLBACK_SUCCESS
-
-    {% for meth in methods.iter() -%}
-    {% let method_name = format!("invoke_{}", meth.name())|fn_name -%}
-    if method == {{ loop.index }}:
-        # Call the method and handle any errors
-        # See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs` for details
-        try:
-            return {{ method_name }}(cb, _UniffiRustBufferStream(args_data, args_len), buf_ptr)
-        except BaseException as e:
-            # Catch unexpected errors
-            try:
-                # Try to serialize the exception into a String
-                buf_ptr[0] = {{ Type::String.borrow()|lower_fn }}(repr(e))
-            except:
-                # If that fails, just give up
-                pass
-            return _UNIFFI_CALLBACK_UNEXPECTED_ERROR
-    {% endfor %}
-
-    # This should never happen, because an out of bounds method index won't
-    # ever be used. Once we can catch errors, we should return an InternalException.
-    # https://github.com/mozilla/uniffi-rs/issues/351
-
-    # An unexpected error happened.
-    # See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-    return _UNIFFI_CALLBACK_UNEXPECTED_ERROR
-
-# We need to keep this function reference alive:
-# if they get GC'd while in use then UniFFI internals could attempt to call a function
-# that is in freed memory.
-# That would be...uh...bad. Yeah, that's the word. Bad.
-{{ callback_handler_obj }} = _UNIFFI_FOREIGN_CALLBACK_T({{ callback_handler_class }})
-_UniffiLib.{{ ffi_init_callback.name() }}({{ callback_handler_obj }})
+    {%- endfor %}
+
+    @{{ "CallbackInterfaceFree"|ffi_callback_name }}
+    def uniffi_free(uniffi_handle):
+        {{ ffi_converter_name }}._handle_map.remove(uniffi_handle)
+
+    # Generate the FFI VTable.  This has a field for each callback interface method.
+    uniffi_vtable = {{ vtable|ffi_type_name }}(
+        {%- for (_, meth) in vtable_methods.iter() %}
+        {{ meth.name()|fn_name }},
+        {%- endfor %}
+        uniffi_free
+    )
+    # Send Rust a pointer to the VTable.  Note: this means we need to keep the struct alive forever,
+    # or else bad things will happen when Rust tries to access it.
+    _UniffiLib.{{ ffi_init_callback.name() }}(ctypes.byref(uniffi_vtable))
diff --git a/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceTemplate.py b/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceTemplate.py
index ab9e725a05..a41e58e635 100644
--- a/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceTemplate.py
+++ b/uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceTemplate.py
@@ -1,10 +1,10 @@
 {%- let cbi = ci|get_callback_interface_definition(name) %}
-{%- let callback_handler_class = format!("UniffiCallbackInterface{}", name) %}
-{%- let callback_handler_obj = format!("uniffiCallbackInterface{}", name) %}
 {%- let ffi_init_callback = cbi.ffi_init_callback() %}
 {%- let protocol_name = type_name.clone() %}
-{%- let methods = cbi.methods() %}
 {%- let protocol_docstring = cbi.docstring() %}
+{%- let vtable = cbi.vtable() %}
+{%- let methods = cbi.methods() %}
+{%- let vtable_methods = cbi.vtable_methods() %}
 
 {% include "Protocol.py" %}
 {% include "CallbackInterfaceImpl.py" %}
diff --git a/uniffi_bindgen/src/bindings/python/templates/Helpers.py b/uniffi_bindgen/src/bindings/python/templates/Helpers.py
index e8eeff7b8a..b4dad8da12 100644
--- a/uniffi_bindgen/src/bindings/python/templates/Helpers.py
+++ b/uniffi_bindgen/src/bindings/python/templates/Helpers.py
@@ -16,15 +16,15 @@ class _UniffiRustCallStatus(ctypes.Structure):
     # These match the values from the uniffi::rustcalls module
     CALL_SUCCESS = 0
     CALL_ERROR = 1
-    CALL_PANIC = 2
+    CALL_UNEXPECTED_ERROR = 2
 
     def __str__(self):
         if self.code == _UniffiRustCallStatus.CALL_SUCCESS:
             return "_UniffiRustCallStatus(CALL_SUCCESS)"
         elif self.code == _UniffiRustCallStatus.CALL_ERROR:
             return "_UniffiRustCallStatus(CALL_ERROR)"
-        elif self.code == _UniffiRustCallStatus.CALL_PANIC:
-            return "_UniffiRustCallStatus(CALL_PANIC)"
+        elif self.code == _UniffiRustCallStatus.CALL_UNEXPECTED_ERROR:
+            return "_UniffiRustCallStatus(CALL_UNEXPECTED_ERROR)"
         else:
             return "_UniffiRustCallStatus(<invalid code>)"
 
@@ -53,7 +53,7 @@ def _uniffi_check_call_status(error_ffi_converter, call_status):
             raise InternalError("_rust_call_with_error: CALL_ERROR, but error_ffi_converter is None")
         else:
             raise error_ffi_converter.lift(call_status.error_buf)
-    elif call_status.code == _UniffiRustCallStatus.CALL_PANIC:
+    elif call_status.code == _UniffiRustCallStatus.CALL_UNEXPECTED_ERROR:
         # When the rust code sees a panic, it tries to construct a _UniffiRustBuffer
         # with the message.  But if that code panics, then it just sends back
         # an empty buffer.
@@ -66,7 +66,21 @@ def _uniffi_check_call_status(error_ffi_converter, call_status):
         raise InternalError("Invalid _UniffiRustCallStatus code: {}".format(
             call_status.code))
 
-# A function pointer for a callback as defined by UniFFI.
-# Rust definition `fn(handle: u64, method: u32, args: _UniffiRustBuffer, buf_ptr: *mut _UniffiRustBuffer) -> int`
-_UNIFFI_FOREIGN_CALLBACK_T = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_ulonglong, ctypes.c_ulong, ctypes.POINTER(ctypes.c_char), ctypes.c_int, ctypes.POINTER(_UniffiRustBuffer))
+def _uniffi_trait_interface_call(call_status, make_call, write_return_value):
+    try:
+        return write_return_value(make_call())
+    except Exception as e:
+        import traceback
+        call_status.code = _UniffiRustCallStatus.CALL_UNEXPECTED_ERROR
+        call_status.error_buf = {{ Type::String.borrow()|lower_fn }}(repr(e))
 
+def _uniffi_trait_interface_call_with_error(call_status, make_call, write_return_value, error_type, lower_error):
+    try:
+        try:
+            return write_return_value(make_call())
+        except error_type as e:
+            call_status.code = _UniffiRustCallStatus.CALL_ERROR
+            call_status.error_buf = lower_error(e)
+    except Exception as e:
+        call_status.code = _UniffiRustCallStatus.CALL_UNEXPECTED_ERROR
+        call_status.error_buf = {{ Type::String.borrow()|lower_fn }}(repr(e))
diff --git a/uniffi_bindgen/src/bindings/python/templates/NamespaceLibraryTemplate.py b/uniffi_bindgen/src/bindings/python/templates/NamespaceLibraryTemplate.py
index 3e5450ad12..3845d8a8b9 100644
--- a/uniffi_bindgen/src/bindings/python/templates/NamespaceLibraryTemplate.py
+++ b/uniffi_bindgen/src/bindings/python/templates/NamespaceLibraryTemplate.py
@@ -63,9 +63,22 @@ def _uniffi_check_api_checksums(lib):
     {%- for arg in callback.arguments() -%}
     {{ arg.type_().borrow()|ffi_type_name }},
     {%- endfor -%}
+    {%- if callback.has_rust_call_status_arg() %}
+    ctypes.POINTER(_UniffiRustCallStatus),
+    {%- endif %}
 )
 {%- endfor %}
 
+# Define FFI structs
+{%- for ffi_struct in ci.ffi_struct_definitions() %}
+class {{ ffi_struct.name()|ffi_struct_name }}(ctypes.Structure):
+    _fields_ = [
+        {%- for field in ffi_struct.fields() %}
+        ("{{ field.name()|var_name }}", {{ field.type_().borrow()|ffi_type_name }}),
+        {%- endfor %}
+    ]
+{%- endfor %}
+
 # A ctypes library to expose the extern-C FFI definitions.
 # This is an implementation detail which will be called internally by the public API.
 
diff --git a/uniffi_bindgen/src/bindings/python/templates/ObjectTemplate.py b/uniffi_bindgen/src/bindings/python/templates/ObjectTemplate.py
index 6efb739156..ddcb9246bf 100644
--- a/uniffi_bindgen/src/bindings/python/templates/ObjectTemplate.py
+++ b/uniffi_bindgen/src/bindings/python/templates/ObjectTemplate.py
@@ -76,9 +76,9 @@ def __ne__(self, other: object) -> {{ ne.return_type().unwrap()|type_name }}:
 {% endfor %}
 
 {%- if obj.has_callback_interface() %}
-{%- let callback_handler_class = format!("UniffiCallbackInterface{}", name) %}
-{%- let callback_handler_obj = format!("uniffiCallbackInterface{}", name) %}
 {%- let ffi_init_callback = obj.ffi_init_callback() %}
+{%- let vtable = obj.vtable().expect("trait interface should have a vtable") %}
+{%- let vtable_methods = obj.vtable_methods() %}
 {% include "CallbackInterfaceImpl.py" %}
 {%- endif %}
 
diff --git a/uniffi_bindgen/src/bindings/ruby/gen_ruby/mod.rs b/uniffi_bindgen/src/bindings/ruby/gen_ruby/mod.rs
index de2deb4410..002c3a963b 100644
--- a/uniffi_bindgen/src/bindings/ruby/gen_ruby/mod.rs
+++ b/uniffi_bindgen/src/bindings/ruby/gen_ruby/mod.rs
@@ -153,9 +153,13 @@ mod filters {
             FfiType::RustBuffer(_) => "RustBuffer.by_value".to_string(),
             FfiType::ForeignBytes => "ForeignBytes".to_string(),
             FfiType::Callback(_) => unimplemented!("FFI Callbacks not implemented"),
-            // Callback interfaces are not yet implemented, but this needs to return something in
-            // order for the coverall tests to pass.
-            FfiType::ForeignCallback => ":pointer".to_string(),
+            // Note: references are not really used by the Ruby bindings yet, maybe this should
+            // change to a different type when they are actually implemented.
+            FfiType::Reference(_) => ":pointer".to_string(),
+            FfiType::VoidPointer => ":pointer".to_string(),
+            FfiType::Struct(_) => {
+                unimplemented!("Structs are not implemented")
+            }
             FfiType::RustFutureHandle | FfiType::RustFutureContinuationData => {
                 unimplemented!("Async functions are not implemented")
             }
diff --git a/uniffi_bindgen/src/bindings/swift/gen_swift/mod.rs b/uniffi_bindgen/src/bindings/swift/gen_swift/mod.rs
index 9ba0e67820..14d1c01a0d 100644
--- a/uniffi_bindgen/src/bindings/swift/gen_swift/mod.rs
+++ b/uniffi_bindgen/src/bindings/swift/gen_swift/mod.rs
@@ -507,12 +507,17 @@ impl SwiftCodeOracle {
         nm.to_string().to_lower_camel_case()
     }
 
-    /// Get the idiomatic Python rendering of an FFI callback function
+    /// Get the idiomatic Swift rendering of an FFI callback function name
     fn ffi_callback_name(&self, nm: &str) -> String {
         format!("Uniffi{}", nm.to_upper_camel_case())
     }
 
-    fn ffi_type_label_raw(&self, ffi_type: &FfiType) -> String {
+    /// Get the idiomatic Swift rendering of an FFI struct name
+    fn ffi_struct_name(&self, nm: &str) -> String {
+        format!("Uniffi{}", nm.to_upper_camel_case())
+    }
+
+    fn ffi_type_label(&self, ffi_type: &FfiType) -> String {
         match ffi_type {
             FfiType::Int8 => "Int8".into(),
             FfiType::UInt8 => "UInt8".into(),
@@ -528,26 +533,18 @@ impl SwiftCodeOracle {
             FfiType::RustBuffer(_) => "RustBuffer".into(),
             FfiType::ForeignBytes => "ForeignBytes".into(),
             FfiType::Callback(name) => self.ffi_callback_name(name),
-            FfiType::ForeignCallback => "ForeignCallback".into(),
-            FfiType::RustFutureHandle | FfiType::RustFutureContinuationData => {
-                "UnsafeMutableRawPointer".into()
+            FfiType::Struct(name) => self.ffi_struct_name(name),
+            FfiType::Reference(inner) => {
+                format!("UnsafeMutablePointer<{}>", self.ffi_type_label(inner))
             }
-        }
-    }
-
-    fn ffi_type_label(&self, ffi_type: &FfiType) -> String {
-        match ffi_type {
-            FfiType::ForeignCallback
+            FfiType::VoidPointer
             | FfiType::RustFutureHandle
-            | FfiType::RustFutureContinuationData => {
-                format!("{} _Nonnull", self.ffi_type_label_raw(ffi_type))
-            }
-            _ => self.ffi_type_label_raw(ffi_type),
+            | FfiType::RustFutureContinuationData => "UnsafeMutableRawPointer".into(),
         }
     }
 
     fn ffi_canonical_name(&self, ffi_type: &FfiType) -> String {
-        self.ffi_type_label_raw(ffi_type)
+        self.ffi_type_label(ffi_type)
     }
 
     /// Get the name of the protocol and class name for an object.
@@ -641,10 +638,11 @@ pub mod filters {
             FfiType::Callback(name) => {
                 format!("{} _Nonnull", SwiftCodeOracle.ffi_callback_name(name))
             }
-            FfiType::ForeignCallback => "ForeignCallback _Nonnull".into(),
-            FfiType::RustFutureHandle | FfiType::RustFutureContinuationData => {
-                "void* _Nonnull".into()
-            }
+            FfiType::Struct(name) => SwiftCodeOracle.ffi_struct_name(name),
+            FfiType::Reference(inner) => format!("{}* _Nonnull", header_ffi_type_name(inner)?),
+            FfiType::VoidPointer
+            | FfiType::RustFutureHandle
+            | FfiType::RustFutureContinuationData => "void* _Nonnull".into(),
         })
     }
 
@@ -679,11 +677,16 @@ pub mod filters {
         Ok(oracle().enum_variant_name(nm))
     }
 
-    /// Get the idiomatic Swift rendering of an ffi callback function name
+    /// Get the idiomatic Swift rendering of an FFI callback function name
     pub fn ffi_callback_name(nm: &str) -> Result<String, askama::Error> {
         Ok(oracle().ffi_callback_name(nm))
     }
 
+    /// Get the idiomatic Swift rendering of an FFI struct name
+    pub fn ffi_struct_name(nm: &str) -> Result<String, askama::Error> {
+        Ok(oracle().ffi_struct_name(nm))
+    }
+
     /// Get the idiomatic Swift rendering of docstring
     pub fn docstring(docstring: &str, spaces: &i32) -> Result<String, askama::Error> {
         let middle = textwrap::indent(&textwrap::dedent(docstring), " * ");
diff --git a/uniffi_bindgen/src/bindings/swift/templates/BridgingHeaderTemplate.h b/uniffi_bindgen/src/bindings/swift/templates/BridgingHeaderTemplate.h
index 352b804993..0c0a81652a 100644
--- a/uniffi_bindgen/src/bindings/swift/templates/BridgingHeaderTemplate.h
+++ b/uniffi_bindgen/src/bindings/swift/templates/BridgingHeaderTemplate.h
@@ -29,8 +29,6 @@ typedef struct RustBuffer
     uint8_t *_Nullable data;
 } RustBuffer;
 
-typedef int32_t (*ForeignCallback)(uint64_t, int32_t, const uint8_t *_Nonnull, int32_t, RustBuffer *_Nonnull);
-
 typedef struct ForeignBytes
 {
     int32_t len;
@@ -50,15 +48,27 @@ typedef struct RustCallStatus {
 // Define FFI callback types
 {%- for callback in ci.ffi_callback_definitions() %}
 typedef
-    {%- match callback.return_type() %}{% when Some(return_type) %} {{ return_type|ffi_type_name }} {% when None %} void {% endmatch -%}
+    {%- match callback.return_type() %}{% when Some(return_type) %} {{ return_type|header_ffi_type_name }} {% when None %} void {% endmatch -%}
     (*{{ callback.name()|ffi_callback_name }})(
         {%- for arg in callback.arguments() -%}
         {{ arg.type_().borrow()|header_ffi_type_name }}
-        {%- if !loop.last %}, {% endif %}
+        {%- if !loop.last || callback.has_rust_call_status_arg() %}, {% endif %}
         {%- endfor -%}
+        {%- if callback.has_rust_call_status_arg() %}
+        RustCallStatus *_Nonnull uniffiCallStatus
+        {%- endif %}
     );
 {%- endfor %}
 
+// Define FFI structs
+{%- for struct in ci.ffi_struct_definitions() %}
+typedef struct {{ struct.name()|ffi_struct_name }} {
+    {%- for field in struct.fields() %}
+    {{ field.type_().borrow()|header_ffi_type_name }} {{ field.name()|var_name }};
+    {%- endfor %}
+} {{ struct.name()|ffi_struct_name }};
+{%- endfor %}
+
 // Scaffolding functions
 {%- for func in ci.iter_ffi_function_definitions() %}
 {% match func.return_type() -%}{%- when Some with (type_) %}{{ type_|header_ffi_type_name }}{% when None %}void{% endmatch %} {{ func.name() }}(
diff --git a/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceImpl.swift b/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceImpl.swift
index 53760a90a9..91d1d854e2 100644
--- a/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceImpl.swift
+++ b/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceImpl.swift
@@ -1,88 +1,61 @@
 {%- if self.include_once_check("CallbackInterfaceRuntime.swift") %}{%- include "CallbackInterfaceRuntime.swift" %}{%- endif %}
-
-// Declaration and FfiConverters for {{ type_name }} Callback Interface
-
-fileprivate let {{ callback_handler }} : ForeignCallback =
-    { (handle: UniFFICallbackHandle, method: Int32, argsData: UnsafePointer<UInt8>, argsLen: Int32, out_buf: UnsafeMutablePointer<RustBuffer>) -> Int32 in
-    {% for meth in methods.iter() -%}
-    {%- let method_name = format!("invoke_{}", meth.name())|fn_name %}
-
-    func {{ method_name }}(_ swiftCallbackInterface: {{ type_name }}, _ argsData: UnsafePointer<UInt8>, _ argsLen: Int32, _ out_buf: UnsafeMutablePointer<RustBuffer>) throws -> Int32 {
-        {%- if meth.arguments().len() > 0 %}
-        var reader = createReader(data: Data(bytes: argsData, count: Int(argsLen)))
-        {%- endif %}
-
-        {%- match meth.return_type() %}
-        {%- when Some(return_type) %}
-        func makeCall() throws -> Int32 {
-            let result = {% if meth.throws() %} try{% endif %} swiftCallbackInterface.{{ meth.name()|fn_name }}(
-                    {% for arg in meth.arguments() -%}
-                    {% if !config.omit_argument_labels() %}{{ arg.name()|var_name }}: {% endif %} try {{ arg|read_fn }}(from: &reader)
-                    {%- if !loop.last %}, {% endif %}
-                    {% endfor -%}
-                )
-            var writer = [UInt8]()
-            {{ return_type|write_fn }}(result, into: &writer)
-            out_buf.pointee = RustBuffer(bytes: writer)
-            return UNIFFI_CALLBACK_SUCCESS
-        }
-        {%- when None %}
-        func makeCall() throws -> Int32 {
-            {% if meth.throws() %}try {% endif %}swiftCallbackInterface.{{ meth.name()|fn_name }}(
-                    {% for arg in meth.arguments() -%}
-                    {% if !config.omit_argument_labels() %}{{ arg.name()|var_name }}: {% endif %} try {{ arg|read_fn }}(from: &reader)
-                    {%- if !loop.last %}, {% endif %}
-                    {% endfor -%}
-                )
-            return UNIFFI_CALLBACK_SUCCESS
-        }
-        {%- endmatch %}
-
-        {%- match meth.throws_type() %}
-        {%- when None %}
-        return try makeCall()
-        {%- when Some(error_type) %}
-        do {
-            return try makeCall()
-        } catch let error as {{ error_type|type_name }} {
-            out_buf.pointee = {{ error_type|lower_fn }}(error)
-            return UNIFFI_CALLBACK_ERROR
-        }
-        {%- endmatch %}
-    }
-    {%- endfor %}
-
-
-    switch method {
-        case IDX_CALLBACK_FREE:
-            {{ ffi_converter_name }}.handleMap.remove(handle: handle)
-            // Successful return
-            // See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-            return UNIFFI_CALLBACK_SUCCESS
-        {% for meth in methods.iter() -%}
-        {% let method_name = format!("invoke_{}", meth.name())|fn_name -%}
-        case {{ loop.index }}:
-            guard let cb = {{ ffi_converter_name }}.handleMap.get(handle: handle) else {
-                out_buf.pointee = {{ Type::String.borrow()|lower_fn }}("No callback in handlemap; this is a Uniffi bug")
-                return UNIFFI_CALLBACK_UNEXPECTED_ERROR
-            }
-            do {
-                return try {{ method_name }}(cb, argsData, argsLen, out_buf)
-            } catch let error {
-                out_buf.pointee = {{ Type::String.borrow()|lower_fn }}(String(describing: error))
-                return UNIFFI_CALLBACK_UNEXPECTED_ERROR
+{%- let trait_impl=format!("UniffiCallbackInterface{}", name) %}
+
+// Put the implementation in a struct so we don't pollute the top-level namespace
+fileprivate struct {{ trait_impl }} {
+
+    // Create the VTable using a series of closures.
+    // Swift automatically converts these into C callback functions.
+    static var vtable: {{ vtable|ffi_type_name }} = {{ vtable|ffi_type_name }}(
+        {%- for (ffi_callback, meth) in vtable_methods %}
+        {{ meth.name()|fn_name }}: { (
+            {%- for arg in ffi_callback.arguments() %}
+            {{ arg.name()|var_name }}: {{ arg.type_().borrow()|ffi_type_name }},
+            {%- endfor -%}
+            {%- if ffi_callback.has_rust_call_status_arg() %}
+            uniffiCallStatus: UnsafeMutablePointer<RustCallStatus>
+            {%- endif %}
+        ) in
+            guard let uniffiObj = {{ ffi_converter_name }}.handleMap.get(handle: uniffiHandle) else {
+                uniffiCallStatus.pointee.code = CALL_UNEXPECTED_ERROR
+                uniffiCallStatus.pointee.errorBuf = {{ Type::String.borrow()|lower_fn }}("No callback in handlemap; this is a Uniffi bug")
+                return
             }
-        {% endfor %}
-        // This should never happen, because an out of bounds method index won't
-        // ever be used. Once we can catch errors, we should return an InternalError.
-        // https://github.com/mozilla/uniffi-rs/issues/351
-        default:
-            // An unexpected error happened.
-            // See docs of ForeignCallback in `uniffi_core/src/ffi/foreigncallbacks.rs`
-            return UNIFFI_CALLBACK_UNEXPECTED_ERROR
-    }
+            let makeCall = { {% if meth.throws() %}try {% endif %}uniffiObj.{{ meth.name()|fn_name }}(
+                {%- for arg in meth.arguments() %}
+                {% if !config.omit_argument_labels() %} {{ arg.name()|arg_name }}: {% endif %}try {{ arg|lift_fn }}({{ arg.name()|var_name }}){% if !loop.last %},{% endif %}
+                {%- endfor %}
+            ) }
+            {% match meth.return_type() %}
+            {%- when Some(t) %}
+            let writeReturn = { uniffiOutReturn.pointee = {{ t|lower_fn }}($0) }
+            {%- when None %}
+            let writeReturn = { () }
+            {%- endmatch %}
+
+            {%- match meth.throws_type() %}
+            {%- when None %}
+            uniffiTraitInterfaceCall(
+                callStatus: uniffiCallStatus,
+                makeCall: makeCall,
+                writeReturn: writeReturn
+            )
+            {%- when Some(error_type) %}
+            uniffiTraitInterfaceCallWithError(
+                callStatus: uniffiCallStatus,
+                makeCall: makeCall,
+                writeReturn: writeReturn,
+                lowerError: {{ error_type|lower_fn }}
+            )
+            {%- endmatch %}
+        },
+        {%- endfor %}
+        uniffiFree: { (uniffiHandle: UInt64) -> () in
+            {{ ffi_converter_name }}.handleMap.delete(handle: uniffiHandle)
+        }
+    )
 }
 
 private func {{ callback_init }}() {
-    {{ ffi_init_callback.name() }}({{ callback_handler }})
+    {{ ffi_init_callback.name() }}(&{{ trait_impl }}.vtable)
 }
diff --git a/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceTemplate.swift b/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceTemplate.swift
index f985ae3cd3..8cdd735b9a 100644
--- a/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceTemplate.swift
+++ b/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceTemplate.swift
@@ -4,6 +4,8 @@
 {%- let methods = cbi.methods() %}
 {%- let protocol_name = type_name.clone() %}
 {%- let protocol_docstring = cbi.docstring() %}
+{%- let vtable = cbi.vtable() %}
+{%- let vtable_methods = cbi.vtable_methods() %}
 {%- let ffi_init_callback = cbi.ffi_init_callback() %}
 
 {% include "Protocol.swift" %}
diff --git a/uniffi_bindgen/src/bindings/swift/templates/Helpers.swift b/uniffi_bindgen/src/bindings/swift/templates/Helpers.swift
index 31b2dadfc2..d233d4b762 100644
--- a/uniffi_bindgen/src/bindings/swift/templates/Helpers.swift
+++ b/uniffi_bindgen/src/bindings/swift/templates/Helpers.swift
@@ -28,7 +28,7 @@ fileprivate enum UniffiInternalError: LocalizedError {
 
 fileprivate let CALL_SUCCESS: Int8 = 0
 fileprivate let CALL_ERROR: Int8 = 1
-fileprivate let CALL_PANIC: Int8 = 2
+fileprivate let CALL_UNEXPECTED_ERROR: Int8 = 2
 fileprivate let CALL_CANCELLED: Int8 = 3
 
 fileprivate extension RustCallStatus {
@@ -81,7 +81,7 @@ private func uniffiCheckCallStatus(
                 throw UniffiInternalError.unexpectedRustCallError
             }
 
-        case CALL_PANIC:
+        case CALL_UNEXPECTED_ERROR:
             // When the rust code sees a panic, it tries to construct a RustBuffer
             // with the message.  But if that code panics, then it just sends back
             // an empty buffer.
@@ -99,3 +99,33 @@ private func uniffiCheckCallStatus(
             throw UniffiInternalError.unexpectedRustCallStatusCode
     }
 }
+
+private func uniffiTraitInterfaceCall<T>(
+    callStatus: UnsafeMutablePointer<RustCallStatus>,
+    makeCall: () throws -> T,
+    writeReturn: (T) -> ()
+) {
+    do {
+        try writeReturn(makeCall())
+    } catch let error {
+        callStatus.pointee.code = CALL_UNEXPECTED_ERROR
+        callStatus.pointee.errorBuf = {{ Type::String.borrow()|lower_fn }}(String(describing: error))
+    }
+}
+
+private func uniffiTraitInterfaceCallWithError<T, E>(
+    callStatus: UnsafeMutablePointer<RustCallStatus>,
+    makeCall: () throws -> T,
+    writeReturn: (T) -> (),
+    lowerError: (E) -> RustBuffer
+) {
+    do {
+        try writeReturn(makeCall())
+    } catch let error as E {
+        callStatus.pointee.code = CALL_ERROR
+        callStatus.pointee.errorBuf = lowerError(error)
+    } catch {
+        callStatus.pointee.code = CALL_UNEXPECTED_ERROR
+        callStatus.pointee.errorBuf = {{ Type::String.borrow()|lower_fn }}(String(describing: error))
+    }
+}
diff --git a/uniffi_bindgen/src/bindings/swift/templates/ObjectTemplate.swift b/uniffi_bindgen/src/bindings/swift/templates/ObjectTemplate.swift
index 518beb5aa0..fc5d47516e 100644
--- a/uniffi_bindgen/src/bindings/swift/templates/ObjectTemplate.swift
+++ b/uniffi_bindgen/src/bindings/swift/templates/ObjectTemplate.swift
@@ -146,6 +146,8 @@ public class {{ impl_class_name }}:
 {%- if obj.has_callback_interface() %}
 {%- let callback_handler = format!("uniffiCallbackInterface{}", name) %}
 {%- let callback_init = format!("uniffiCallbackInit{}", name) %}
+{%- let vtable = obj.vtable().expect("trait interface should have a vtable") %}
+{%- let vtable_methods = obj.vtable_methods() %}
 {%- let ffi_init_callback = obj.ffi_init_callback() %}
 {% include "CallbackInterfaceImpl.swift" %}
 {%- endif %}
diff --git a/uniffi_bindgen/src/interface/callbacks.rs b/uniffi_bindgen/src/interface/callbacks.rs
index 9573e07932..90c34a9c17 100644
--- a/uniffi_bindgen/src/interface/callbacks.rs
+++ b/uniffi_bindgen/src/interface/callbacks.rs
@@ -33,9 +33,11 @@
 //! # Ok::<(), anyhow::Error>(())
 //! ```
 
+use std::iter;
+
 use uniffi_meta::Checksum;
 
-use super::ffi::FfiFunction;
+use super::ffi::{FfiArgument, FfiCallbackFunction, FfiField, FfiFunction, FfiStruct, FfiType};
 use super::object::Method;
 use super::{AsType, Type, TypeIterator};
 
@@ -70,7 +72,32 @@ impl CallbackInterface {
     }
 
     pub(super) fn derive_ffi_funcs(&mut self) {
-        self.ffi_init_callback = FfiFunction::callback_init(&self.module_path, &self.name);
+        self.ffi_init_callback =
+            FfiFunction::callback_init(&self.module_path, &self.name, vtable_name(&self.name));
+    }
+
+    /// FfiCallbacks to define for our methods.
+    pub fn ffi_callbacks(&self) -> Vec<FfiCallbackFunction> {
+        ffi_callbacks(&self.name, &self.methods)
+    }
+
+    /// The VTable FFI type
+    pub fn vtable(&self) -> FfiType {
+        FfiType::Struct(vtable_name(&self.name))
+    }
+
+    /// the VTable struct to define.
+    pub fn vtable_definition(&self) -> FfiStruct {
+        vtable_struct(&self.name, &self.methods)
+    }
+
+    /// Vec of (ffi_callback, method) pairs
+    pub fn vtable_methods(&self) -> Vec<(FfiCallbackFunction, &Method)> {
+        self.methods
+            .iter()
+            .enumerate()
+            .map(|(i, method)| (method_ffi_callback(&self.name, method, i), method))
+            .collect()
     }
 
     pub fn iter_types(&self) -> TypeIterator<'_> {
@@ -105,6 +132,62 @@ impl TryFrom<uniffi_meta::CallbackInterfaceMetadata> for CallbackInterface {
     }
 }
 
+/// [FfiCallbackFunction] functions for the methods of a callback/trait interface
+pub fn ffi_callbacks(trait_name: &str, methods: &[Method]) -> Vec<FfiCallbackFunction> {
+    methods
+        .iter()
+        .enumerate()
+        .map(|(i, method)| method_ffi_callback(trait_name, method, i))
+        .collect()
+}
+
+pub fn method_ffi_callback(trait_name: &str, method: &Method, index: usize) -> FfiCallbackFunction {
+    FfiCallbackFunction {
+        name: method_ffi_callback_name(trait_name, index),
+        arguments: iter::once(FfiArgument::new("uniffi_handle", FfiType::UInt64))
+            .chain(method.arguments().into_iter().map(Into::into))
+            .chain(iter::once(match method.return_type() {
+                Some(t) => FfiArgument::new("uniffi_out_return", FfiType::from(t).reference()),
+                None => FfiArgument::new("uniffi_out_return", FfiType::VoidPointer),
+            }))
+            .collect(),
+        has_rust_call_status_arg: true,
+        return_type: None,
+    }
+}
+
+/// [FfiStruct] for a callback/trait interface VTable
+///
+/// This struct has a FfiCallbackFunction field for each method, plus extra fields for special
+/// methods
+pub fn vtable_struct(trait_name: &str, methods: &[Method]) -> FfiStruct {
+    FfiStruct {
+        name: vtable_name(trait_name),
+        fields: methods
+            .iter()
+            .enumerate()
+            .map(|(i, method)| {
+                FfiField::new(
+                    method.name(),
+                    FfiType::Callback(format!("CallbackInterface{trait_name}Method{i}")),
+                )
+            })
+            .chain([FfiField::new(
+                "uniffi_free",
+                FfiType::Callback("CallbackInterfaceFree".to_owned()),
+            )])
+            .collect(),
+    }
+}
+
+pub fn method_ffi_callback_name(trait_name: &str, index: usize) -> String {
+    format!("CallbackInterface{trait_name}Method{index}")
+}
+
+pub fn vtable_name(trait_name: &str) -> String {
+    format!("VTableCallbackInterface{trait_name}")
+}
+
 #[cfg(test)]
 mod test {
     use super::super::ComponentInterface;
diff --git a/uniffi_bindgen/src/interface/ffi.rs b/uniffi_bindgen/src/interface/ffi.rs
index 2eeaffe9b7..5ecb582567 100644
--- a/uniffi_bindgen/src/interface/ffi.rs
+++ b/uniffi_bindgen/src/interface/ffi.rs
@@ -47,16 +47,25 @@ pub enum FfiType {
     /// A borrowed reference to some raw bytes owned by foreign language code.
     /// The provider of this reference must keep it alive for the duration of the receiving call.
     ForeignBytes,
-    /// Pointer to a callback function.  The inner type is the name of the callback, which matches
-    /// one of the items in [crate::ComponentInterface::ffi_callback_definitions].
+    /// Pointer to a callback function.  The inner value which matches one of the items in
+    /// [crate::ComponentInterface::ffi_callback_definitions].
     Callback(String),
-    /// Pointer to a callback function that handles all callbacks on the foreign language side.
-    ForeignCallback,
+    /// Pointer to a VTable.  The inner value matches one of the items in
+    /// [crate::ComponentInterface::ffi_struct_definitions].
+    Struct(String),
     /// Pointer to a Rust future
     RustFutureHandle,
     RustFutureContinuationData,
-    // TODO: you can imagine a richer structural typesystem here, e.g. `Ref<String>` or something.
-    // We don't need that yet and it's possible we never will, so it isn't here for now.
+    /// Pointer to an FfiType.
+    Reference(Box<FfiType>),
+    /// Opaque pointer
+    VoidPointer,
+}
+
+impl FfiType {
+    pub fn reference(self) -> FfiType {
+        FfiType::Reference(Box::new(self))
+    }
 }
 
 /// When passing data across the FFI, each `Type` value will be lowered into a corresponding
@@ -150,12 +159,12 @@ pub struct FfiFunction {
 }
 
 impl FfiFunction {
-    pub fn callback_init(module_path: &str, trait_name: &str) -> Self {
+    pub fn callback_init(module_path: &str, trait_name: &str, vtable_name: String) -> Self {
         Self {
-            name: uniffi_meta::init_callback_fn_symbol_name(module_path, trait_name),
+            name: uniffi_meta::init_callback_vtable_fn_symbol_name(module_path, trait_name),
             arguments: vec![FfiArgument {
-                name: "handle".to_string(),
-                type_: FfiType::ForeignCallback,
+                name: "vtable".to_string(),
+                type_: FfiType::Struct(vtable_name).reference(),
             }],
             return_type: None,
             has_rust_call_status_arg: false,
@@ -271,6 +280,49 @@ impl FfiCallbackFunction {
     }
 }
 
+/// Represents a repr(C) struct used in the FFI
+#[derive(Debug, Default, Clone)]
+pub struct FfiStruct {
+    pub(super) name: String,
+    pub(super) fields: Vec<FfiField>,
+}
+
+impl FfiStruct {
+    /// Get the name of the VTable
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Get the (
+    pub fn fields(&self) -> &[FfiField] {
+        &self.fields
+    }
+}
+
+/// Represents a field of an [FfiStruct]
+#[derive(Debug, Clone)]
+pub struct FfiField {
+    pub(super) name: String,
+    pub(super) type_: FfiType,
+}
+
+impl FfiField {
+    pub fn new(name: impl Into<String>, type_: FfiType) -> Self {
+        Self {
+            name: name.into(),
+            type_,
+        }
+    }
+
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    pub fn type_(&self) -> FfiType {
+        self.type_.clone()
+    }
+}
+
 #[cfg(test)]
 mod test {
     // There's not really much to test here to be honest,
diff --git a/uniffi_bindgen/src/interface/mod.rs b/uniffi_bindgen/src/interface/mod.rs
index e6c646becd..823d3672cc 100644
--- a/uniffi_bindgen/src/interface/mod.rs
+++ b/uniffi_bindgen/src/interface/mod.rs
@@ -67,7 +67,7 @@ mod record;
 pub use record::{Field, Record};
 
 pub mod ffi;
-pub use ffi::{FfiArgument, FfiCallbackFunction, FfiFunction, FfiType};
+pub use ffi::{FfiArgument, FfiCallbackFunction, FfiFunction, FfiStruct, FfiType};
 pub use uniffi_meta::Radix;
 use uniffi_meta::{
     ConstructorMetadata, LiteralMetadata, NamespaceMetadata, ObjectMetadata, TraitMethodMetadata,
@@ -216,16 +216,47 @@ impl ComponentInterface {
     /// Get the definitions for callback FFI functions
     ///
     /// These are defined by the foreign code and invoked by Rust.
-    pub fn ffi_callback_definitions(&self) -> impl IntoIterator<Item = FfiCallbackFunction> {
-        [FfiCallbackFunction {
-            name: "RustFutureContinuationCallback".to_owned(),
-            arguments: vec![
-                FfiArgument::new("data", FfiType::RustFutureContinuationData),
-                FfiArgument::new("poll_result", FfiType::Int8),
-            ],
-            return_type: None,
-            has_rust_call_status_arg: false,
-        }]
+    pub fn ffi_callback_definitions(&self) -> impl IntoIterator<Item = FfiCallbackFunction> + '_ {
+        self.builtin_ffi_callback_definitions().into_iter().chain(
+            self.callback_interfaces
+                .iter()
+                .flat_map(|cbi| cbi.ffi_callbacks())
+                .chain(self.objects.iter().flat_map(|o| o.ffi_callbacks())),
+        )
+    }
+
+    fn builtin_ffi_callback_definitions(&self) -> impl IntoIterator<Item = FfiCallbackFunction> {
+        [
+            FfiCallbackFunction {
+                name: "RustFutureContinuationCallback".to_owned(),
+                arguments: vec![
+                    FfiArgument::new("data", FfiType::RustFutureContinuationData),
+                    FfiArgument::new("poll_result", FfiType::Int8),
+                ],
+                return_type: None,
+                has_rust_call_status_arg: false,
+            },
+            FfiCallbackFunction {
+                name: "CallbackInterfaceFree".to_owned(),
+                arguments: vec![FfiArgument::new("handle", FfiType::UInt64)],
+                return_type: None,
+                has_rust_call_status_arg: false,
+            },
+        ]
+    }
+
+    /// Get the definitions for callback FFI functions
+    ///
+    /// These are defined by the foreign code and invoked by Rust.
+    pub fn ffi_struct_definitions(&self) -> impl IntoIterator<Item = FfiStruct> + '_ {
+        self.callback_interface_definitions()
+            .iter()
+            .map(|cbi| cbi.vtable_definition())
+            .chain(
+                self.object_definitions()
+                    .iter()
+                    .flat_map(|o| o.vtable_definition()),
+            )
     }
 
     /// Get the definitions for every Callback Interface type in the interface.
diff --git a/uniffi_bindgen/src/interface/object.rs b/uniffi_bindgen/src/interface/object.rs
index 84778dd53b..48b4c34e1d 100644
--- a/uniffi_bindgen/src/interface/object.rs
+++ b/uniffi_bindgen/src/interface/object.rs
@@ -60,7 +60,8 @@
 use anyhow::Result;
 use uniffi_meta::Checksum;
 
-use super::ffi::{FfiArgument, FfiFunction, FfiType};
+use super::callbacks;
+use super::ffi::{FfiArgument, FfiCallbackFunction, FfiFunction, FfiStruct, FfiType};
 use super::function::{Argument, Callable};
 use super::{AsType, ObjectImpl, Type, TypeIterator};
 
@@ -219,8 +220,11 @@ impl Object {
         self.ffi_func_free.return_type = None;
         self.ffi_func_free.is_object_free_function = true;
         if self.has_callback_interface() {
-            self.ffi_init_callback =
-                Some(FfiFunction::callback_init(&self.module_path, &self.name));
+            self.ffi_init_callback = Some(FfiFunction::callback_init(
+                &self.module_path,
+                &self.name,
+                callbacks::vtable_name(&self.name),
+            ));
         }
 
         for cons in self.constructors.iter_mut() {
@@ -236,6 +240,41 @@ impl Object {
         Ok(())
     }
 
+    /// For trait interfaces, FfiCallbacks to define for our methods, otherwise an empty vec.
+    pub fn ffi_callbacks(&self) -> Vec<FfiCallbackFunction> {
+        if self.is_trait_interface() {
+            callbacks::ffi_callbacks(&self.name, &self.methods)
+        } else {
+            vec![]
+        }
+    }
+
+    /// For trait interfaces, the VTable FFI type
+    pub fn vtable(&self) -> Option<FfiType> {
+        self.is_trait_interface()
+            .then(|| FfiType::Struct(callbacks::vtable_name(&self.name)))
+    }
+
+    /// For trait interfaces, the VTable struct to define.  Otherwise None.
+    pub fn vtable_definition(&self) -> Option<FfiStruct> {
+        self.is_trait_interface()
+            .then(|| callbacks::vtable_struct(&self.name, &self.methods))
+    }
+
+    /// Vec of (ffi_callback_name, method) pairs
+    pub fn vtable_methods(&self) -> Vec<(FfiCallbackFunction, &Method)> {
+        self.methods
+            .iter()
+            .enumerate()
+            .map(|(i, method)| {
+                (
+                    callbacks::method_ffi_callback(&self.name, method, i),
+                    method,
+                )
+            })
+            .collect()
+    }
+
     pub fn iter_types(&self) -> TypeIterator<'_> {
         Box::new(
             self.methods
diff --git a/uniffi_core/src/ffi/callbackinterface.rs b/uniffi_core/src/ffi/callbackinterface.rs
index 41c85dcac8..e7a4faab64 100644
--- a/uniffi_core/src/ffi/callbackinterface.rs
+++ b/uniffi_core/src/ffi/callbackinterface.rs
@@ -91,122 +91,20 @@
 //!
 //! Uniffi generates a protocol or interface in client code in the foreign language must implement.
 //!
-//! For each callback interface, a `CallbackInternals` (on the Foreign Language side) and `ForeignCallbackInternals`
-//! (on Rust side) manages the process through a `ForeignCallback`. There is one `ForeignCallback` per callback interface.
+//! For each callback interface, UniFFI defines a VTable.
+//! This is a `repr(C)` struct where each field is a `repr(C)` callback function pointer.
+//! There is one field for each method, plus an extra field for the `uniffi_free` method.
+//! The foreign code registers one VTable per callback interface with Rust.
 //!
-//! Passing a callback interface implementation from foreign language (e.g. `AndroidKeychain`) into Rust causes the
-//! `KeychainCallbackInternals` to store the instance in a handlemap.
-//!
-//! The object handle is passed over to Rust, and used to instantiate a struct `KeychainProxy` which implements
-//! the trait. This proxy implementation is generate by Uniffi. The `KeychainProxy` object is then passed to
-//! client code as `Box<dyn Keychain>`.
-//!
-//! Methods on `KeychainProxy` objects (e.g. `self.keychain.get("username".into())`) encode the arguments into a `RustBuffer`.
-//! Using the `ForeignCallback`, it calls the `CallbackInternals` object on the foreign language side using the
-//! object handle, and the method selector.
-//!
-//! The `CallbackInternals` object unpacks the arguments from the passed buffer, gets the object out from the handlemap,
-//! and calls the actual implementation of the method.
-//!
-//! If there's a return value, it is packed up in to another `RustBuffer` and used as the return value for
-//! `ForeignCallback`. The caller of `ForeignCallback`, the `KeychainProxy` unpacks the returned buffer into the correct
-//! type and then returns to client code.
+//! VTable methods have a similar signature to Rust scaffolding functions.
+//! The one difference is that values are returned via an out pointer to work around a Python bug (https://bugs.python.org/issue5710).
 //!
+//! The foreign object that implements the interface is represented by an opaque handle.
+//! UniFFI generates a struct that implements the trait by calling VTable methods, passing the handle as the first parameter.
+//! When the struct is dropped, the `uniffi_free` method is called.
 
-use crate::{ForeignCallback, ForeignCallbackCell, Lift, LiftReturn, RustBuffer};
 use std::fmt;
 
-/// The method index used by the Drop trait to communicate to the foreign language side that Rust has finished with it,
-/// and it can be deleted from the handle map.
-pub const IDX_CALLBACK_FREE: u32 = 0;
-
-/// Result of a foreign callback invocation
-#[repr(i32)]
-#[derive(Debug, PartialEq, Eq)]
-pub enum CallbackResult {
-    /// Successful call.
-    /// The return value is serialized to `buf_ptr`.
-    Success = 0,
-    /// Expected error.
-    /// This is returned when a foreign method throws an exception that corresponds to the Rust Err half of a Result.
-    /// The error value is serialized to `buf_ptr`.
-    Error = 1,
-    /// Unexpected error.
-    /// An error message string is serialized to `buf_ptr`.
-    UnexpectedError = 2,
-}
-
-impl TryFrom<i32> for CallbackResult {
-    // On errors we return the unconverted value
-    type Error = i32;
-
-    fn try_from(value: i32) -> Result<Self, i32> {
-        match value {
-            0 => Ok(Self::Success),
-            1 => Ok(Self::Error),
-            2 => Ok(Self::UnexpectedError),
-            n => Err(n),
-        }
-    }
-}
-
-/// Struct to hold a foreign callback.
-pub struct ForeignCallbackInternals {
-    callback_cell: ForeignCallbackCell,
-}
-
-impl ForeignCallbackInternals {
-    pub const fn new() -> Self {
-        ForeignCallbackInternals {
-            callback_cell: ForeignCallbackCell::new(),
-        }
-    }
-
-    pub fn set_callback(&self, callback: ForeignCallback) {
-        self.callback_cell.set(callback);
-    }
-
-    /// Invoke a callback interface method on the foreign side and return the result
-    pub fn invoke_callback<R, UniFfiTag>(&self, handle: u64, method: u32, args: RustBuffer) -> R
-    where
-        R: LiftReturn<UniFfiTag>,
-    {
-        let mut ret_rbuf = RustBuffer::new();
-        let callback = self.callback_cell.get();
-        let raw_result = unsafe {
-            callback(
-                handle,
-                method,
-                args.data_pointer(),
-                args.len() as i32,
-                &mut ret_rbuf,
-            )
-        };
-        RustBuffer::destroy(args);
-        let result = CallbackResult::try_from(raw_result)
-            .unwrap_or_else(|code| panic!("Callback failed with unexpected return code: {code}"));
-        match result {
-            CallbackResult::Success => R::lift_callback_return(ret_rbuf),
-            CallbackResult::Error => R::lift_callback_error(ret_rbuf),
-            CallbackResult::UnexpectedError => {
-                let reason = if !ret_rbuf.is_empty() {
-                    match <String as Lift<UniFfiTag>>::try_lift(ret_rbuf) {
-                        Ok(s) => s,
-                        Err(e) => {
-                            log::error!("{{ trait_name }} Error reading ret_buf: {e}");
-                            String::from("[Error reading reason]")
-                        }
-                    }
-                } else {
-                    RustBuffer::destroy(ret_rbuf);
-                    String::from("[Unknown Reason]")
-                };
-                R::handle_callback_unexpected_error(UnexpectedUniFFICallbackError { reason })
-            }
-        }
-    }
-}
-
 /// Used when internal/unexpected error happened when calling a foreign callback, for example when
 /// a unknown exception is raised
 ///
@@ -217,8 +115,10 @@ pub struct UnexpectedUniFFICallbackError {
 }
 
 impl UnexpectedUniFFICallbackError {
-    pub fn from_reason(reason: String) -> Self {
-        Self { reason }
+    pub fn new(reason: impl fmt::Display) -> Self {
+        Self {
+            reason: reason.to_string(),
+        }
     }
 }
 
diff --git a/uniffi_core/src/ffi/foreigncallbacks.rs b/uniffi_core/src/ffi/foreigncallbacks.rs
index 68d9a0d9b1..326ff12747 100644
--- a/uniffi_core/src/ffi/foreigncallbacks.rs
+++ b/uniffi_core/src/ffi/foreigncallbacks.rs
@@ -8,73 +8,32 @@
 //! code loads the exported library. For each callback type, we also define a "cell" type for
 //! storing the callback.
 
-use std::sync::atomic::{AtomicUsize, Ordering};
-
-use crate::RustBuffer;
-
-/// ForeignCallback is the Rust representation of a foreign language function.
-/// It is the basis for all callbacks interfaces. It is registered exactly once per callback interface,
-/// at library start up time.
-/// Calling this method is only done by generated objects which mirror callback interfaces objects in the foreign language.
-///
-/// * The `handle` is the key into a handle map on the other side of the FFI used to look up the foreign language object
-///   that implements the callback interface/trait.
-/// * The `method` selector specifies the method that will be called on the object, by looking it up in a list of methods from
-///   the IDL. The list is 1 indexed. Note that the list of methods is generated by UniFFI from the IDL and used in all
-///   bindings, so we can rely on the method list being stable within the same run of UniFFI.
-/// * `args_data` and `args_len` represents a serialized buffer of arguments to the function. The scaffolding code
-///   writes the callback arguments to this buffer, in order, using `FfiConverter.write()`. The bindings code reads the
-///   arguments from the buffer and passes them to the user's callback.
-/// * `buf_ptr` is a pointer to where the resulting buffer will be written. UniFFI will allocate a
-///   buffer to write the result into.
-/// * Callbacks return one of the `CallbackResult` values
-///   Note: The output buffer might still contain 0 bytes of data.
-pub type ForeignCallback = unsafe extern "C" fn(
-    handle: u64,
-    method: u32,
-    args_data: *const u8,
-    args_len: i32,
-    buf_ptr: *mut RustBuffer,
-) -> i32;
-
-/// Store a [ForeignCallback] pointer
-pub(crate) struct ForeignCallbackCell(AtomicUsize);
-
-/// Macro to define foreign callback types as well as the callback cell.
-macro_rules! impl_foreign_callback_cell {
-    ($callback_type:ident, $cell_type:ident) => {
-        // Overly-paranoid sanity checking to ensure that these types are
-        // convertible between each-other. `transmute` actually should check this for
-        // us too, but this helps document the invariants we rely on in this code.
-        //
-        // Note that these are guaranteed by
-        // https://rust-lang.github.io/unsafe-code-guidelines/layout/function-pointers.html
-        // and thus this is a little paranoid.
-        static_assertions::assert_eq_size!(usize, $callback_type);
-        static_assertions::assert_eq_size!(usize, Option<$callback_type>);
-
-        impl $cell_type {
-            pub const fn new() -> Self {
-                Self(AtomicUsize::new(0))
-            }
-
-            pub fn set(&self, callback: $callback_type) {
-                // Store the pointer using Ordering::Relaxed.  This is sufficient since callback
-                // should be set at startup, before there's any chance of using them.
-                self.0.store(callback as usize, Ordering::Relaxed);
-            }
-
-            pub fn get(&self) -> $callback_type {
-                let ptr_value = self.0.load(Ordering::Relaxed);
-                unsafe {
-                    // SAFETY: self.0 was set in `set` from our function pointer type, so
-                    // it's safe to transmute it back here.
-                    ::std::mem::transmute::<usize, Option<$callback_type>>(ptr_value)
-                        .expect("Bug: callback not set.  This is likely a uniffi bug.")
-                }
-            }
+use std::{
+    ptr::{null_mut, NonNull},
+    sync::atomic::{AtomicPtr, Ordering},
+};
+
+// Cell type that stores any NonNull<T>
+#[doc(hidden)]
+pub struct UniffiForeignPointerCell<T>(AtomicPtr<T>);
+
+impl<T> UniffiForeignPointerCell<T> {
+    pub const fn new() -> Self {
+        Self(AtomicPtr::new(null_mut()))
+    }
+
+    pub fn set(&self, callback: NonNull<T>) {
+        self.0.store(callback.as_ptr(), Ordering::Relaxed);
+    }
+
+    pub fn get(&self) -> &T {
+        unsafe {
+            NonNull::new(self.0.load(Ordering::Relaxed))
+                .expect("Foreign pointer not set.  This is likely a uniffi bug.")
+                .as_mut()
         }
-    };
+    }
 }
 
-impl_foreign_callback_cell!(ForeignCallback, ForeignCallbackCell);
+unsafe impl<T> Send for UniffiForeignPointerCell<T> {}
+unsafe impl<T> Sync for UniffiForeignPointerCell<T> {}
diff --git a/uniffi_core/src/ffi/rustcalls.rs b/uniffi_core/src/ffi/rustcalls.rs
index 51204ef261..16b0c76f2e 100644
--- a/uniffi_core/src/ffi/rustcalls.rs
+++ b/uniffi_core/src/ffi/rustcalls.rs
@@ -56,6 +56,13 @@ pub struct RustCallStatus {
 }
 
 impl RustCallStatus {
+    pub fn new() -> Self {
+        Self {
+            code: RustCallStatusCode::Success,
+            error_buf: MaybeUninit::new(RustBuffer::new()),
+        }
+    }
+
     pub fn cancelled() -> Self {
         Self {
             code: RustCallStatusCode::Cancelled,
diff --git a/uniffi_core/src/ffi_converter_impls.rs b/uniffi_core/src/ffi_converter_impls.rs
index 5be5f04da5..aec093154a 100644
--- a/uniffi_core/src/ffi_converter_impls.rs
+++ b/uniffi_core/src/ffi_converter_impls.rs
@@ -456,7 +456,11 @@ unsafe impl<UT> LowerReturn<UT> for () {
 }
 
 unsafe impl<UT> LiftReturn<UT> for () {
-    fn lift_callback_return(_buf: RustBuffer) -> Self {}
+    type ReturnType = ();
+
+    fn try_lift_successful_return(_: ()) -> Result<Self> {
+        Ok(())
+    }
 
     const TYPE_ID_META: MetadataBuffer = MetadataBuffer::from_code(metadata::codes::TYPE_UNIT);
 }
@@ -493,13 +497,15 @@ where
 unsafe impl<UT, R, E> LiftReturn<UT> for Result<R, E>
 where
     R: LiftReturn<UT>,
-    E: Lift<UT> + ConvertError<UT>,
+    E: Lift<UT, FfiType = RustBuffer> + ConvertError<UT>,
 {
-    fn lift_callback_return(buf: RustBuffer) -> Self {
-        Ok(R::lift_callback_return(buf))
+    type ReturnType = R::ReturnType;
+
+    fn try_lift_successful_return(v: R::ReturnType) -> Result<Self> {
+        R::try_lift_successful_return(v).map(Ok)
     }
 
-    fn lift_callback_error(buf: RustBuffer) -> Self {
+    fn lift_error(buf: RustBuffer) -> Self {
         match E::try_lift_from_rust_buffer(buf) {
             Ok(lifted_error) => Err(lifted_error),
             Err(anyhow_error) => {
diff --git a/uniffi_core/src/ffi_converter_traits.rs b/uniffi_core/src/ffi_converter_traits.rs
index 3b5914e32f..987a47c414 100644
--- a/uniffi_core/src/ffi_converter_traits.rs
+++ b/uniffi_core/src/ffi_converter_traits.rs
@@ -51,7 +51,10 @@ use std::{borrow::Borrow, sync::Arc};
 use anyhow::bail;
 use bytes::Buf;
 
-use crate::{FfiDefault, MetadataBuffer, Result, RustBuffer, UnexpectedUniFFICallbackError};
+use crate::{
+    FfiDefault, MetadataBuffer, Result, RustBuffer, RustCallStatus, RustCallStatusCode,
+    UnexpectedUniFFICallbackError,
+};
 
 /// Generalized FFI conversions
 ///
@@ -302,14 +305,41 @@ pub unsafe trait LowerReturn<UT>: Sized {
 /// These traits should not be used directly, only in generated code, and the generated code should
 /// have fixture tests to test that everything works correctly together.
 pub unsafe trait LiftReturn<UT>: Sized {
-    /// Lift a Rust value for a callback interface method result
-    fn lift_callback_return(buf: RustBuffer) -> Self;
+    /// FFI return type for trait interfaces
+    type ReturnType;
+
+    /// Lift a successfully returned value from a trait interface
+    fn try_lift_successful_return(v: Self::ReturnType) -> Result<Self>;
+
+    /// Lift a foreign returned value from a trait interface
+    ///
+    /// When we call a foreign-implemented trait interface method, we pass a &mut RustCallStatus
+    /// and get [Self::ReturnType] returned.  This method takes both of those and lifts `Self` from
+    /// it.
+    fn lift_foreign_return(ffi_return: Self::ReturnType, call_status: RustCallStatus) -> Self {
+        match call_status.code {
+            RustCallStatusCode::Success => Self::try_lift_successful_return(ffi_return)
+                .unwrap_or_else(|e| {
+                    Self::handle_callback_unexpected_error(UnexpectedUniFFICallbackError::new(e))
+                }),
+            RustCallStatusCode::Error => {
+                Self::lift_error(unsafe { call_status.error_buf.assume_init() })
+            }
+            _ => {
+                let e = <String as FfiConverter<crate::UniFfiTag>>::try_lift(unsafe {
+                    call_status.error_buf.assume_init()
+                })
+                .unwrap_or_else(|e| format!("(Error lifting message: {e}"));
+                Self::handle_callback_unexpected_error(UnexpectedUniFFICallbackError::new(e))
+            }
+        }
+    }
 
     /// Lift a Rust value for a callback interface method error result
     ///
     /// This is called for "expected errors" -- the callback method returns a Result<> type and the
     /// foreign code throws an exception that corresponds to the error type.
-    fn lift_callback_error(_buf: RustBuffer) -> Self {
+    fn lift_error(_buf: RustBuffer) -> Self {
         panic!("Callback interface method returned unexpected error")
     }
 
@@ -439,9 +469,10 @@ macro_rules! derive_ffi_traits {
     (impl $(<$($generic:ident),*>)? $(::uniffi::)? LiftReturn<$ut:path> for $ty:ty $(where $($where:tt)*)?) => {
         unsafe impl $(<$($generic),*>)* $crate::LiftReturn<$ut> for $ty $(where $($where)*)*
         {
-            fn lift_callback_return(buf: $crate::RustBuffer) -> Self {
-                <Self as $crate::Lift<$ut>>::try_lift_from_rust_buffer(buf)
-                    .expect("Error reading callback interface result")
+            type ReturnType = <Self as $crate::Lift<$ut>>::FfiType;
+
+            fn try_lift_successful_return(v: Self::ReturnType) -> $crate::Result<Self> {
+                <Self as $crate::Lift<$ut>>::try_lift(v)
             }
 
             const TYPE_ID_META: $crate::MetadataBuffer = <Self as $crate::Lift<$ut>>::TYPE_ID_META;
diff --git a/uniffi_macros/src/export/callback_interface.rs b/uniffi_macros/src/export/callback_interface.rs
index 576df52c98..966b84d0a2 100644
--- a/uniffi_macros/src/export/callback_interface.rs
+++ b/uniffi_macros/src/export/callback_interface.rs
@@ -10,10 +10,16 @@ use crate::{
     },
 };
 use proc_macro2::{Span, TokenStream};
-use quote::quote;
+use quote::{format_ident, quote};
 use std::iter;
 use syn::Ident;
 
+/// Generate a trait impl that calls foreign callbacks
+///
+/// This generates:
+///    * A `repr(C)` VTable struct where each field is the FFI function for the trait method.
+///    * A FFI function for foreign code to set their VTable for the interface
+///    * An implementation of the trait using that VTable
 pub(super) fn trait_impl(
     mod_path: &str,
     trait_ident: &Ident,
@@ -21,30 +27,51 @@ pub(super) fn trait_impl(
 ) -> syn::Result<TokenStream> {
     let trait_name = ident_to_string(trait_ident);
     let trait_impl_ident = trait_impl_ident(&trait_name);
-    let internals_ident = internals_ident(&trait_name);
+    let vtable_type = format_ident!("UniFfiTraitVtable{trait_name}");
+    let vtable_cell = format_ident!("UNIFFI_TRAIT_CELL_{}", trait_name.to_uppercase());
     let init_ident = Ident::new(
-        &uniffi_meta::init_callback_fn_symbol_name(mod_path, &trait_name),
+        &uniffi_meta::init_callback_vtable_fn_symbol_name(mod_path, &trait_name),
         Span::call_site(),
     );
-
-    let trait_impl_methods = items
+    let methods = items
         .iter()
         .map(|item| match item {
-            ImplItem::Method(sig) => gen_method_impl(sig, &internals_ident),
-            _ => unreachable!("traits have no constructors"),
+            ImplItem::Constructor(sig) => Err(syn::Error::new(
+                sig.span,
+                "Constructors not allowed in trait interfaces",
+            )),
+            ImplItem::Method(sig) => Ok(sig),
         })
-        .collect::<syn::Result<TokenStream>>()?;
+        .collect::<syn::Result<Vec<_>>>()?;
+
+    let vtable_fields = methods.iter()
+        .map(|sig| {
+            let ident = &sig.ident;
+            let params = sig.scaffolding_params();
+            let lift_return = sig.lift_return_impl();
+            quote! {
+                #ident: extern "C" fn(handle: u64, #(#params,)* &mut #lift_return::ReturnType, &mut ::uniffi::RustCallStatus),
+            }
+        });
+
+    let trait_impl_methods = methods
+        .iter()
+        .map(|sig| gen_method_impl(sig, &vtable_cell))
+        .collect::<syn::Result<Vec<_>>>()?;
+
     Ok(quote! {
-        #[doc(hidden)]
-        static #internals_ident: ::uniffi::ForeignCallbackInternals = ::uniffi::ForeignCallbackInternals::new();
+        struct #vtable_type {
+            #(#vtable_fields)*
+            uniffi_dec_ref: extern "C" fn(handle: u64),
+        }
+
+        static #vtable_cell: ::uniffi::UniffiForeignPointerCell::<#vtable_type> = ::uniffi::UniffiForeignPointerCell::<#vtable_type>::new();
 
-        #[doc(hidden)]
         #[no_mangle]
-        pub extern "C" fn #init_ident(callback: ::uniffi::ForeignCallback) {
-            #internals_ident.set_callback(callback);
+        extern "C" fn #init_ident(vtable: ::std::ptr::NonNull<#vtable_type>) {
+            #vtable_cell.set(vtable);
         }
 
-        #[doc(hidden)]
         #[derive(Debug)]
         struct #trait_impl_ident {
             handle: u64,
@@ -56,18 +83,17 @@ pub(super) fn trait_impl(
             }
         }
 
-        impl ::std::ops::Drop for #trait_impl_ident {
-            fn drop(&mut self) {
-                #internals_ident.invoke_callback::<(), crate::UniFfiTag>(
-                    self.handle, uniffi::IDX_CALLBACK_FREE, Default::default()
-                )
-            }
-        }
-
         ::uniffi::deps::static_assertions::assert_impl_all!(#trait_impl_ident: ::core::marker::Send);
 
         impl #trait_ident for #trait_impl_ident {
-            #trait_impl_methods
+            #(#trait_impl_methods)*
+        }
+
+        impl ::std::ops::Drop for #trait_impl_ident {
+            fn drop(&mut self) {
+                let vtable = #vtable_cell.get();
+                (vtable.uniffi_dec_ref)(self.handle);
+            }
         }
     })
 }
@@ -79,16 +105,6 @@ pub fn trait_impl_ident(trait_name: &str) -> Ident {
     )
 }
 
-pub fn internals_ident(trait_name: &str) -> Ident {
-    Ident::new(
-        &format!(
-            "UNIFFI_FOREIGN_CALLBACK_INTERNALS_{}",
-            trait_name.to_ascii_uppercase()
-        ),
-        Span::call_site(),
-    )
-}
-
 pub fn ffi_converter_callback_interface_impl(
     trait_ident: &Ident,
     trait_impl_ident: &Ident,
@@ -131,49 +147,55 @@ pub fn ffi_converter_callback_interface_impl(
     }
 }
 
-fn gen_method_impl(sig: &FnSignature, internals_ident: &Ident) -> syn::Result<TokenStream> {
+/// Generate a single method for [trait_impl].  This implements a trait method by invoking a
+/// foreign-supplied callback.
+fn gen_method_impl(sig: &FnSignature, vtable_cell: &Ident) -> syn::Result<TokenStream> {
     let FnSignature {
         ident,
         return_ty,
         kind,
         receiver,
+        name,
+        span,
         ..
     } = sig;
-    let index = match kind {
-        // Note: the callback index is 1-based, since 0 is reserved for the free function
-        FnKind::TraitMethod { index, .. } => index + 1,
-        k => {
-            return Err(syn::Error::new(
-                sig.span,
-                format!(
-                    "Internal UniFFI error: Unexpected function kind for callback interface {k:?}"
-                ),
-            ));
-        }
-    };
+
+    if !matches!(kind, FnKind::TraitMethod { .. }) {
+        return Err(syn::Error::new(
+            *span,
+            format!(
+                "Internal UniFFI error: Unexpected function kind for callback interface {name}: {kind:?}",
+            ),
+        ));
+    }
 
     let self_param = match receiver {
+        Some(ReceiverArg::Ref) => quote! { &self },
+        Some(ReceiverArg::Arc) => quote! { self: Arc<Self> },
         None => {
             return Err(syn::Error::new(
-                sig.span,
+                *span,
                 "callback interface methods must take &self as their first argument",
             ));
         }
-        Some(ReceiverArg::Ref) => quote! { &self },
-        Some(ReceiverArg::Arc) => quote! { self: Arc<Self> },
     };
+
     let params = sig.params();
-    let buf_ident = Ident::new("uniffi_args_buf", Span::call_site());
-    let write_exprs = sig.write_exprs(&buf_ident);
+    let lower_exprs = sig.args.iter().map(|a| {
+        let lower_impl = a.lower_impl();
+        let ident = &a.ident;
+        quote! { #lower_impl::lower(#ident) }
+    });
+
+    let lift_return = sig.lift_return_impl();
 
     Ok(quote! {
         fn #ident(#self_param, #(#params),*) -> #return_ty {
-            #[allow(unused_mut)]
-            let mut #buf_ident = ::std::vec::Vec::new();
-            #(#write_exprs;)*
-            let uniffi_args_rbuf = uniffi::RustBuffer::from_vec(#buf_ident);
-
-            #internals_ident.invoke_callback::<#return_ty, crate::UniFfiTag>(self.handle, #index, uniffi_args_rbuf)
+            let vtable = #vtable_cell.get();
+            let mut uniffi_call_status = ::uniffi::RustCallStatus::new();
+            let mut return_value: #lift_return::ReturnType = ::uniffi::FfiDefault::ffi_default();
+            (vtable.#ident)(self.handle, #(#lower_exprs,)* &mut return_value, &mut uniffi_call_status);
+            #lift_return::lift_foreign_return(return_value, uniffi_call_status)
         }
     })
 }
diff --git a/uniffi_macros/src/export/scaffolding.rs b/uniffi_macros/src/export/scaffolding.rs
index aec4916de8..0e0da87a2e 100644
--- a/uniffi_macros/src/export/scaffolding.rs
+++ b/uniffi_macros/src/export/scaffolding.rs
@@ -231,7 +231,7 @@ pub(super) fn gen_ffi_function(
 
     let ffi_ident = sig.scaffolding_fn_ident()?;
     let name = &sig.name;
-    let return_impl = &sig.return_impl();
+    let return_impl = &sig.lower_return_impl();
 
     Ok(if !sig.is_async {
         quote! {
diff --git a/uniffi_macros/src/fnsig.rs b/uniffi_macros/src/fnsig.rs
index bcf1e21876..cc554da856 100644
--- a/uniffi_macros/src/fnsig.rs
+++ b/uniffi_macros/src/fnsig.rs
@@ -111,13 +111,20 @@ impl FnSignature {
         })
     }
 
-    pub fn return_impl(&self) -> TokenStream {
+    pub fn lower_return_impl(&self) -> TokenStream {
         let return_ty = &self.return_ty;
         quote! {
             <#return_ty as ::uniffi::LowerReturn<crate::UniFfiTag>>
         }
     }
 
+    pub fn lift_return_impl(&self) -> TokenStream {
+        let return_ty = &self.return_ty;
+        quote! {
+            <#return_ty as ::uniffi::LiftReturn<crate::UniFfiTag>>
+        }
+    }
+
     /// Generate a closure that tries to lift all arguments into a tuple.
     ///
     /// The closure moves all scaffolding arguments into itself and returns:
@@ -162,14 +169,6 @@ impl FnSignature {
         quote! { #(#args),* }
     }
 
-    /// Write expressions for each of our arguments
-    pub fn write_exprs<'a>(
-        &'a self,
-        buf_ident: &'a Ident,
-    ) -> impl Iterator<Item = TokenStream> + 'a {
-        self.args.iter().map(|a| a.write_expr(buf_ident))
-    }
-
     /// Parameters expressions for each of our arguments
     pub fn params(&self) -> impl Iterator<Item = TokenStream> + '_ {
         self.args.iter().map(NamedArg::param)
@@ -501,13 +500,6 @@ impl NamedArg {
         quote! { #ident: #lift_impl::FfiType }
     }
 
-    /// Generate the expression to write the scaffolding parameter for this arg
-    pub(crate) fn write_expr(&self, buf_ident: &Ident) -> TokenStream {
-        let ident = &self.ident;
-        let lower_impl = self.lower_impl();
-        quote! { #lower_impl::write(#ident, &mut #buf_ident) }
-    }
-
     pub(crate) fn arg_metadata(&self) -> TokenStream {
         let name = &self.name;
         let lift_impl = self.lift_impl();
diff --git a/uniffi_meta/src/ffi_names.rs b/uniffi_meta/src/ffi_names.rs
index a58977b790..5c931a09e3 100644
--- a/uniffi_meta/src/ffi_names.rs
+++ b/uniffi_meta/src/ffi_names.rs
@@ -46,9 +46,12 @@ pub fn free_fn_symbol_name(namespace: &str, object_name: &str) -> String {
 }
 
 /// FFI symbol name for the `init_callback` function for a callback interface
-pub fn init_callback_fn_symbol_name(namespace: &str, callback_interface_name: &str) -> String {
+pub fn init_callback_vtable_fn_symbol_name(
+    namespace: &str,
+    callback_interface_name: &str,
+) -> String {
     let callback_interface_name = callback_interface_name.to_ascii_lowercase();
-    format!("uniffi_{namespace}_fn_init_callback_{callback_interface_name}")
+    format!("uniffi_{namespace}_fn_init_callback_vtable_{callback_interface_name}")
 }
 
 /// FFI checksum symbol name for a top-level function