diff --git a/CMakeLists.txt b/CMakeLists.txt
index c334534250777..01a2c9da4df2b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -265,11 +265,11 @@ set(SWIFT_ANDROID_DEPLOY_DEVICE_PATH "" CACHE STRING
   "Path on an Android device where build products will be pushed. These are used when running the test suite against the device")
 
 #
-# User-configurable ICU specific options for Android, FreeBSD, Linux and Haiku.
+# User-configurable ICU specific options for Android, FreeBSD, Linux, Haiku, and WASI.
 #
 
-foreach(sdk ANDROID;FREEBSD;LINUX;WINDOWS;HAIKU)
-  foreach(arch aarch64;armv6;armv7;i686;powerpc64;powerpc64le;s390x;x86_64)
+foreach(sdk ANDROID;FREEBSD;LINUX;WINDOWS;HAIKU;WASI)
+  foreach(arch aarch64;armv6;armv7;i686;powerpc64;powerpc64le;s390x;wasm32;x86_64)
     set(SWIFT_${sdk}_${arch}_ICU_UC "" CACHE STRING
         "Path to a directory containing the icuuc library for ${sdk}")
     set(SWIFT_${sdk}_${arch}_ICU_UC_INCLUDE "" CACHE STRING
@@ -610,6 +610,8 @@ else()
     set(SWIFT_HOST_VARIANT_ARCH_default "itanium")
   elseif("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "(x86|i686)")
     set(SWIFT_HOST_VARIANT_ARCH_default "i686")
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "wasm32")
+    set(SWIFT_HOST_VARIANT_ARCH_default "wasm32")
   else()
     message(FATAL_ERROR "Unrecognized architecture on host system: ${CMAKE_SYSTEM_PROCESSOR}")
   endif()
@@ -794,6 +796,12 @@ if(swift_build_windows AND NOT "${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
   configure_sdk_windows("Windows" "msvc" "${SWIFT_SDK_WINDOWS_ARCHITECTURES}")
 endif()
 
+# Should we cross-compile the standard library for WASI?
+is_sdk_requested(WASI swift_build_wasm)
+if(swift_build_wasm AND NOT "${SWIFT_HOST_VARIANT_SDK}" STREQUAL "WASI")
+  configure_sdk_unix(WASI wasm32)
+endif()
+
 if("${SWIFT_SDKS}" STREQUAL "")
   set(SWIFT_SDKS "${SWIFT_CONFIGURED_SDKS}")
 endif()
diff --git a/cmake/modules/SwiftConfigureSDK.cmake b/cmake/modules/SwiftConfigureSDK.cmake
index 5953feca4b9fd..51aceb3d2a797 100644
--- a/cmake/modules/SwiftConfigureSDK.cmake
+++ b/cmake/modules/SwiftConfigureSDK.cmake
@@ -230,6 +230,8 @@ macro(configure_sdk_unix name architectures)
   set(SWIFT_SDK_${prefix}_ARCHITECTURES "${architectures}")
   if("${prefix}" STREQUAL "CYGWIN")
     set(SWIFT_SDK_${prefix}_OBJECT_FORMAT "COFF")
+  elseif("${prefix}" STREQUAL "WASI")
+    set(SWIFT_SDK_${prefix}_OBJECT_FORMAT "WASM")
   else()
     set(SWIFT_SDK_${prefix}_OBJECT_FORMAT "ELF")
   endif()
@@ -357,6 +359,14 @@ macro(configure_sdk_unix name architectures)
           message(FATAL_ERROR "unsupported arch for Haiku: ${arch}")
         endif()
         set(SWIFT_SDK_HAIKU_ARCH_x86_64_TRIPLE "x86_64-unknown-haiku")
+      elseif("${prefix}" STREQUAL "WASI")
+        if(NOT arch STREQUAL wasm32)
+          message(FATAL_ERROR "unsupported arch for WebAssembly: ${arch}")
+        endif()
+        set(SWIFT_SDK_WASI_ARCH_wasm32_PATH "${SWIFT_WASI_SDK_PATH}/share/wasi-sysroot")
+        set(SWIFT_SDK_WASI_ARCH_wasm32_TRIPLE "wasm32-unknown-wasi")
+        set(SWIFT_SDK_WASI_ARCH_wasm32_LIBC_INCLUDE_DIRECTORY "${SWIFT_WASI_SDK_PATH}/share/wasi-sysroot/include")
+        set(SWIFT_SDK_WASI_ARCH_wasm32_LIBC_ARCHITECTURE_INCLUDE_DIRECTORY "${SWIFT_WASI_SDK_PATH}/share/wasi-sysroot/include")
       else()
         message(FATAL_ERROR "unknown Unix OS: ${prefix}")
       endif()
diff --git a/cmake/modules/SwiftSetIfArchBitness.cmake b/cmake/modules/SwiftSetIfArchBitness.cmake
index 2929e50fa0ce0..0203908ffdab3 100644
--- a/cmake/modules/SwiftSetIfArchBitness.cmake
+++ b/cmake/modules/SwiftSetIfArchBitness.cmake
@@ -12,7 +12,8 @@ function(set_if_arch_bitness var_name)
      "${SIA_ARCH}" STREQUAL "armv6" OR
      "${SIA_ARCH}" STREQUAL "armv7" OR
      "${SIA_ARCH}" STREQUAL "armv7k" OR
-     "${SIA_ARCH}" STREQUAL "armv7s")
+     "${SIA_ARCH}" STREQUAL "armv7s" OR
+     "${SIA_ARCH}" STREQUAL "wasm32")
     set("${var_name}" "${SIA_CASE_32_BIT}" PARENT_SCOPE)
   elseif("${SIA_ARCH}" STREQUAL "x86_64" OR
          "${SIA_ARCH}" STREQUAL "amd64" OR
diff --git a/stdlib/cmake/modules/AddSwiftStdlib.cmake b/stdlib/cmake/modules/AddSwiftStdlib.cmake
index 6114a6785eb0e..1d0f99557d033 100644
--- a/stdlib/cmake/modules/AddSwiftStdlib.cmake
+++ b/stdlib/cmake/modules/AddSwiftStdlib.cmake
@@ -307,6 +307,10 @@ function(_add_target_variant_c_compile_flags)
     endif()
   endif()
 
+  if("${CFLAGS_SDK}" STREQUAL "WASI")
+    list(APPEND result "-D_WASI_EMULATED_MMAN")
+  endif()
+
   set("${CFLAGS_RESULT_VAR_NAME}" "${result}" PARENT_SCOPE)
 endfunction()
 
@@ -1407,6 +1411,9 @@ endfunction()
 # SWIFT_MODULE_DEPENDS_HAIKU
 #   Swift modules this library depends on when built for Haiku.
 #
+# SWIFT_MODULE_DEPENDS_WASI
+#   Swift modules this library depends on when built for WASI.
+#
 # FRAMEWORK_DEPENDS
 #   System frameworks this library depends on.
 #
@@ -1519,6 +1526,7 @@ function(add_swift_target_library name)
         SWIFT_MODULE_DEPENDS_LINUX
         SWIFT_MODULE_DEPENDS_OSX
         SWIFT_MODULE_DEPENDS_TVOS
+        SWIFT_MODULE_DEPENDS_WASI
         SWIFT_MODULE_DEPENDS_WATCHOS
         SWIFT_MODULE_DEPENDS_WINDOWS
         SWIFT_MODULE_DEPENDS_FROM_SDK
@@ -1684,6 +1692,9 @@ function(add_swift_target_library name)
     elseif(${sdk} STREQUAL HAIKU)
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_HAIKU})
+    elseif(${sdk} STREQUAL WASI)
+      list(APPEND swiftlib_module_depends_flattened
+           ${SWIFTLIB_SWIFT_MODULE_DEPENDS_WASI})
     elseif(${sdk} STREQUAL WINDOWS)
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_WINDOWS})