diff --git a/lib/core.js b/lib/core.js
index 590bc1dc798..d224ecc44ba 100644
--- a/lib/core.js
+++ b/lib/core.js
@@ -908,3 +908,5 @@ declare var console: {
     warn(...data: Array<any>): void,
     ...
 };
+
+declare var globalThis: $GlobalThis;
\ No newline at end of file
diff --git a/src/typing/coverage.ml b/src/typing/coverage.ml
index a233fdbbefe..c664af782b7 100644
--- a/src/typing/coverage.ml
+++ b/src/typing/coverage.ml
@@ -189,6 +189,7 @@ class visitor = object (self)
     | FunProtoApplyT _
     | FunProtoBindT _
     | FunProtoCallT _
+    | GlobalThisT _
     | InternalT _
     | KeysT _
     | MaybeT _
diff --git a/src/typing/debug_js.ml b/src/typing/debug_js.ml
index c4722c28113..32f561f763c 100644
--- a/src/typing/debug_js.ml
+++ b/src/typing/debug_js.ml
@@ -173,6 +173,7 @@ and _json_of_t_impl json_cx t = Hh_json.(
   | FunProtoApplyT _
   | FunProtoBindT _
   | FunProtoCallT _
+  | GlobalThisT _
     -> []
 
   | DefT (_, _, FunT (static, proto, funtype)) -> [
@@ -1796,7 +1797,8 @@ let rec dump_t_ (depth, tvars) cx t =
   | FunProtoT _
   | FunProtoApplyT _
   | FunProtoBindT _
-  | FunProtoCallT _ -> p t
+  | FunProtoCallT _ 
+  | GlobalThisT _ -> p t
   | DefT (_, trust, PolyT (_, tps, c, id)) -> p ~trust:(Some trust) ~extra:(spf "%s [%s] #%d"
       (kid c)
       (String.concat "; " (Core_list.map ~f:(fun tp -> tp.name) (Nel.to_list tps)))
diff --git a/src/typing/flow_js.ml b/src/typing/flow_js.ml
index 27aa6780f33..a979825a8d4 100644
--- a/src/typing/flow_js.ml
+++ b/src/typing/flow_js.ml
@@ -6522,6 +6522,14 @@ let rec __flow cx ((l: Type.t), (u: Type.use_t)) trace =
     | FunProtoCallT reason, _ ->
       rec_flow cx trace (FunProtoT reason, u)
 
+    | GlobalThisT _,
+      SetPropT (_, _, Named (_, name), _, tin, _) ->
+      set_builtin cx ~trace name tin;
+
+    | GlobalThisT _, _ ->
+      let t = builtins cx in
+      rec_flow cx trace (t, u)
+
     | _, LookupT (_, _, _, propref, lookup_action) ->
       let use_op = use_op_of_lookup_action lookup_action in
       add_output cx ~trace (Error_message.EIncompatibleProp {
@@ -7308,7 +7316,8 @@ and any_propagated_use cx trace use_op any l =
   | FunProtoCallT _
   | FunProtoT _
   | ObjProtoT _
-  | NullProtoT _ ->
+  | NullProtoT _
+  | GlobalThisT _ ->
       true
 
   (* Handled already in __flow *)
@@ -7729,6 +7738,7 @@ and check_polarity cx ?trace polarity = function
   | FunProtoApplyT _
   | FunProtoBindT _
   | FunProtoCallT _
+  | GlobalThisT _
   | EvalT _
   | InternalT (ExtendsT _)
   | InternalT (ChoiceKitT _)
diff --git a/src/typing/members.ml b/src/typing/members.ml
index efbe9420eb4..a33b2390647 100644
--- a/src/typing/members.ml
+++ b/src/typing/members.ml
@@ -431,6 +431,7 @@ let rec extract_type cx this_t = match this_t with
   | FunProtoBindT _
   | FunProtoCallT _
   | FunProtoT _
+  | GlobalThisT _
   | KeysT (_, _)
   | DefT (_, _, MixedT _)
   | NullProtoT _
diff --git a/src/typing/resolvableTypeJob.ml b/src/typing/resolvableTypeJob.ml
index b2381056218..20bb67a7cdf 100644
--- a/src/typing/resolvableTypeJob.ml
+++ b/src/typing/resolvableTypeJob.ml
@@ -251,6 +251,7 @@ and collect_of_type ?log_unresolved cx acc = function
   | FunProtoT _
   | NullProtoT _
   | ObjProtoT _
+  | GlobalThisT _
   | CustomFunT (_, _)
 
   | ExistsT _
diff --git a/src/typing/sigHash.ml b/src/typing/sigHash.ml
index a119ac8895a..5a80dba0018 100644
--- a/src/typing/sigHash.ml
+++ b/src/typing/sigHash.ml
@@ -48,6 +48,7 @@ type hash =
   | FunProtoApplyH
   | FunProtoBindH
   | FunProtoCallH
+  | GlobalThisH
   | ObjH
   | ObjProtoH
   | MatchingPropH
@@ -222,6 +223,7 @@ let hash_of_ctor = Type.(function
   | FunProtoApplyT _ -> FunProtoApplyH
   | FunProtoBindT _ -> FunProtoBindH
   | FunProtoCallT _ -> FunProtoCallH
+  | GlobalThisT _ -> GlobalThisH
   | IntersectionT _ -> IntersectionH
   | KeysT _ -> KeysH
   | MaybeT _ -> MaybeH
diff --git a/src/typing/ty_normalizer.ml b/src/typing/ty_normalizer.ml
index cafdaff6951..65f514672a4 100644
--- a/src/typing/ty_normalizer.ml
+++ b/src/typing/ty_normalizer.ml
@@ -705,6 +705,7 @@ end = struct
     | ModuleT (reason, _, _) -> module_t env reason t
 
     | DefT (_, _, CharSetT _)
+    | GlobalThisT _
     | NullProtoT _ ->
       terr ~kind:UnsupportedTypeCtor (Some t)
 
diff --git a/src/typing/type.ml b/src/typing/type.ml
index f53a38b1ce8..f5703706679 100644
--- a/src/typing/type.ml
+++ b/src/typing/type.ml
@@ -86,7 +86,7 @@ module rec TypeTerm : sig
     (* exact *)
     | ExactT of reason * t
 
-    | FunProtoT of reason      (* Function.prototype *)
+    | FunProtoT of reason       (* Function.prototype *)
     | ObjProtoT of reason       (* Object.prototype *)
 
     (* Signifies the end of the prototype chain. Distinct from NullT when it
@@ -97,6 +97,8 @@ module rec TypeTerm : sig
     | FunProtoBindT of reason   (* Function.prototype.bind *)
     | FunProtoCallT of reason   (* Function.prototype.call *)
 
+    | GlobalThisT of reason      (* globalThis *)
+
     (* generalizations of AnyT *)
     | AnyWithLowerBoundT of t (* any supertype of t *)
     | AnyWithUpperBoundT of t (* any subtype of t *)
@@ -2143,6 +2145,7 @@ end = struct
     | FunProtoApplyT reason -> reason
     | FunProtoBindT reason -> reason
     | FunProtoCallT reason -> reason
+    | GlobalThisT reason -> reason
     | KeysT (reason, _) -> reason
     | ModuleT (reason, _, _) -> reason
     | NullProtoT reason -> reason
@@ -2307,6 +2310,7 @@ end = struct
     | FunProtoT (reason) -> FunProtoT (f reason)
     | FunProtoBindT (reason) -> FunProtoBindT (f reason)
     | FunProtoCallT (reason) -> FunProtoCallT (f reason)
+    | GlobalThisT (reason) -> GlobalThisT (f reason)
     | KeysT (reason, t) -> KeysT (f reason, t)
     | ModuleT (reason, exports, is_strict) -> ModuleT (f reason, exports, is_strict)
     | NullProtoT reason -> NullProtoT (f reason)
@@ -3118,6 +3122,7 @@ let string_of_ctor = function
   | FunProtoApplyT _ -> "FunProtoApplyT"
   | FunProtoBindT _ -> "FunProtoBindT"
   | FunProtoCallT _ -> "FunProtoCallT"
+  | GlobalThisT _ -> "GlobalThisT"
   | KeysT _ -> "KeysT"
   | ModuleT _ -> "ModuleT"
   | NullProtoT _ -> "NullProtoT"
diff --git a/src/typing/type_annotation.ml b/src/typing/type_annotation.ml
index 746fdb97f20..33fa0eb921e 100644
--- a/src/typing/type_annotation.ml
+++ b/src/typing/type_annotation.ml
@@ -851,6 +851,12 @@ let rec convert cx tparams_map = Ast.Type.(function
       reconstruct_ast (AnyT.make Annotated reason) None
     )
 
+  | "$GlobalThis" ->
+    check_type_arg_arity cx loc t_ast targs 0 (fun () ->
+      let reason = mk_reason (RCustom "global this") loc in
+      reconstruct_ast (GlobalThisT reason) None
+    )
+
   | "Function$Prototype$Apply" ->
     check_type_arg_arity cx loc t_ast targs 0 (fun () ->
       let reason = mk_reason RFunctionType loc in
diff --git a/src/typing/type_mapper.ml b/src/typing/type_mapper.ml
index 04f7ce8c309..d4b470fdd04 100644
--- a/src/typing/type_mapper.ml
+++ b/src/typing/type_mapper.ml
@@ -107,7 +107,8 @@ class virtual ['a] t = object(self)
       | NullProtoT _
       | FunProtoApplyT _
       | FunProtoBindT _
-      | FunProtoCallT _ -> t
+      | FunProtoCallT _ 
+      | GlobalThisT _ -> t
       | AnyWithLowerBoundT t' ->
           let t'' = self#type_ cx map_cx t' in
           if t'' == t' then t
diff --git a/src/typing/type_visitor.ml b/src/typing/type_visitor.ml
index fc14976c7e4..7fc5319e6ed 100644
--- a/src/typing/type_visitor.ml
+++ b/src/typing/type_visitor.ml
@@ -37,6 +37,7 @@ class ['a] t = object(self)
   | FunProtoCallT _
   | ObjProtoT _
   | NullProtoT _
+  | GlobalThisT _
     -> acc
 
   | CustomFunT (_, kind) -> self#custom_fun_kind cx acc kind