diff --git a/clang/include/clang/Basic/Module.h b/clang/include/clang/Basic/Module.h
--- a/clang/include/clang/Basic/Module.h
+++ b/clang/include/clang/Basic/Module.h
@@ -106,9 +106,15 @@
     /// of header files.
     ModuleMapModule,
 
-    /// This is a C++ Modules TS module interface unit.
+    /// This is a C++ Modules TS or C++20 module interface unit.
     ModuleInterfaceUnit,
 
+    /// This is a C++ 20 module partition interface.
+    ModulePartitionInterface,
+
+    /// This is a C++ 20 module partition implementation.
+    ModulePartitionImplementation,
+
     /// This is a fragment of the global module within some C++ module.
     GlobalModuleFragment,
 
@@ -150,7 +156,10 @@
 
   /// Does this Module scope describe part of the purview of a named C++ module?
   bool isModulePurview() const {
-    return Kind == ModuleInterfaceUnit || Kind == PrivateModuleFragment;
+    return Kind == ModuleInterfaceUnit ||
+           Kind == ModulePartitionInterface ||
+           Kind == ModulePartitionImplementation ||
+           Kind == PrivateModuleFragment;
   }
 
 private:
@@ -502,6 +511,13 @@
     Parent->SubModules.push_back(this);
   }
 
+  /// Is this a module partition.
+  /// ??? : make a bit and stream it?
+
+  bool isPartition() const {
+    return Name.find(':') != std::string::npos;
+  }
+
   /// Retrieve the full name of this module, including the path from
   /// its top-level module.
   /// \param AllowStringLiterals If \c true, components that might not be
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -1546,6 +1546,8 @@
     return nullptr;
 
   case Module::ModuleInterfaceUnit:
+  case Module::ModulePartitionInterface:
+  case Module::ModulePartitionImplementation:
     return M;
 
   case Module::GlobalModuleFragment: {
diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
--- a/clang/lib/Basic/Module.cpp
+++ b/clang/lib/Basic/Module.cpp
@@ -167,6 +167,9 @@
     }
   }
 
+  if (Kind == Module::ModulePartitionImplementation)
+    return false;
+
   llvm_unreachable("could not find a reason why module is unavailable");
 }
 
diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -252,6 +252,8 @@
                                : ModuleScopes.back().Module->Kind) {
   case Module::ModuleMapModule:
   case Module::GlobalModuleFragment:
+  case Module::ModulePartitionImplementation:
+  case Module::ModulePartitionInterface:
     Diag(PrivateLoc, diag::err_private_module_fragment_not_module);
     return nullptr;
 
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -2628,7 +2628,7 @@
   Abbrev->Add(BitCodeAbbrevOp(SUBMODULE_DEFINITION));
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // ID
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Parent
-  Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 2)); // Kind
+  Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3)); // Kind
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsFramework
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsExplicit
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsSystem