diff --git a/toolchain/check/handle_modifier.cpp b/toolchain/check/handle_modifier.cpp
index 75fa2c60b412..3cf89bb312f1 100644
--- a/toolchain/check/handle_modifier.cpp
+++ b/toolchain/check/handle_modifier.cpp
@@ -94,4 +94,14 @@ static auto HandleModifier(Context& context, Parse::NodeId node_id,
   }
 #include "toolchain/parse/node_kind.def"
 
+auto HandleParseNode(Context& context,
+                     Parse::ExternModifierWithLibraryId node_id) -> bool {
+  return context.TODO(node_id, "extern library syntax");
+}
+
+auto HandleParseNode(Context& context, Parse::ExternModifierId node_id)
+    -> bool {
+  return HandleModifier(context, node_id, KeywordModifierSet::Extern);
+}
+
 }  // namespace Carbon::Check
diff --git a/toolchain/check/testdata/function/declaration/no_prelude/extern.carbon b/toolchain/check/testdata/function/declaration/no_prelude/extern.carbon
index 6e4e7b6b204d..8c960562acc6 100644
--- a/toolchain/check/testdata/function/declaration/no_prelude/extern.carbon
+++ b/toolchain/check/testdata/function/declaration/no_prelude/extern.carbon
@@ -44,18 +44,30 @@ fn F();
 
 // --- fail_member_extern.carbon
 
+library "member_extern";
+
 class C {
   // CHECK:STDERR: fail_member_extern.carbon:[[@LINE+4]]:3: ERROR: `extern` not allowed on `fn` declaration that is a member.
   // CHECK:STDERR:   extern fn F();
   // CHECK:STDERR:   ^~~~~~
   // CHECK:STDERR:
   extern fn F();
-  // CHECK:STDERR: fail_member_extern.carbon:[[@LINE+3]]:3: ERROR: `extern` not allowed on `fn` declaration that is a member.
+  // CHECK:STDERR: fail_member_extern.carbon:[[@LINE+4]]:3: ERROR: `extern` not allowed on `fn` declaration that is a member.
   // CHECK:STDERR:   extern fn G[self: Self]();
   // CHECK:STDERR:   ^~~~~~
+  // CHECK:STDERR:
   extern fn G[self: Self]();
 }
 
+// --- fail_todo_extern_library.carbon
+
+library "extern_library";
+
+// CHECK:STDERR: fail_todo_extern_library.carbon:[[@LINE+3]]:1: ERROR: Semantics TODO: `extern library syntax`.
+// CHECK:STDERR: extern library "foo" fn F();
+// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~
+extern library "foo" fn F();
+
 // CHECK:STDOUT: --- basic.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
@@ -132,8 +144,8 @@ class C {
 // CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {}
 // CHECK:STDOUT:   %G.decl: %G.type = fn_decl @G [template = constants.%G] {
 // CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%C [template = constants.%C]
-// CHECK:STDOUT:     %self.loc11_15.1: %C = param self
-// CHECK:STDOUT:     %self.loc11_15.2: %C = bind_name self, %self.loc11_15.1
+// CHECK:STDOUT:     %self.loc14_15.1: %C = param self
+// CHECK:STDOUT:     %self.loc14_15.2: %C = bind_name self, %self.loc14_15.1
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -144,5 +156,9 @@ class C {
 // CHECK:STDOUT:
 // CHECK:STDOUT: fn @F();
 // CHECK:STDOUT:
-// CHECK:STDOUT: fn @G[@C.%self.loc11_15.2: %C]();
+// CHECK:STDOUT: fn @G[@C.%self.loc14_15.2: %C]();
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_todo_extern_library.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {}
 // CHECK:STDOUT:
diff --git a/toolchain/parse/context.cpp b/toolchain/parse/context.cpp
index b79400e385f7..e6ef5457ffbf 100644
--- a/toolchain/parse/context.cpp
+++ b/toolchain/parse/context.cpp
@@ -437,6 +437,43 @@ auto Context::RecoverFromDeclError(StateStackEntry state, NodeKind node_kind,
           /*has_error=*/true);
 }
 
+auto Context::ParseLibraryName(bool accept_default)
+    -> std::optional<StringLiteralValueId> {
+  if (auto library_name_token = ConsumeIf(Lex::TokenKind::StringLiteral)) {
+    AddLeafNode(NodeKind::LibraryName, *library_name_token);
+    return tokens().GetStringLiteralValue(*library_name_token);
+  }
+
+  if (accept_default) {
+    if (auto default_token = ConsumeIf(Lex::TokenKind::Default)) {
+      AddLeafNode(NodeKind::DefaultLibrary, *default_token);
+      return StringLiteralValueId::Invalid;
+    }
+  }
+
+  CARBON_DIAGNOSTIC(
+      ExpectedLibraryNameOrDefault, Error,
+      "Expected `default` or a string literal to specify the library name.");
+  CARBON_DIAGNOSTIC(ExpectedLibraryName, Error,
+                    "Expected a string literal to specify the library name.");
+  emitter().Emit(*position(), accept_default ? ExpectedLibraryNameOrDefault
+                                             : ExpectedLibraryName);
+  return std::nullopt;
+}
+
+auto Context::ParseLibrarySpecifier(bool accept_default)
+    -> std::optional<StringLiteralValueId> {
+  auto library_token = ConsumeChecked(Lex::TokenKind::Library);
+  auto library_subtree_start = tree().size();
+  auto library_id = ParseLibraryName(accept_default);
+  if (!library_id) {
+    AddLeafNode(NodeKind::LibraryName, *position_, /*has_error=*/true);
+  }
+  AddNode(NodeKind::LibrarySpecifier, library_token, library_subtree_start,
+          /*has_error=*/false);
+  return library_id;
+}
+
 auto Context::DiagnoseExpectedDeclSemi(Lex::TokenKind expected_kind) -> void {
   CARBON_DIAGNOSTIC(ExpectedDeclSemi, Error,
                     "`{0}` declarations must end with a `;`.", Lex::TokenKind);
diff --git a/toolchain/parse/context.h b/toolchain/parse/context.h
index 0ccf6f944bba..348265a8079f 100644
--- a/toolchain/parse/context.h
+++ b/toolchain/parse/context.h
@@ -302,6 +302,18 @@ class Context {
   auto RecoverFromDeclError(StateStackEntry state, NodeKind node_kind,
                             bool skip_past_likely_end) -> void;
 
+  // Handles parsing of the library name. Returns the name's ID on success,
+  // which may be invalid for `default`.
+  // TODO: Add an invalid node on error, fix callers to adapt.
+  auto ParseLibraryName(bool accept_default)
+      -> std::optional<StringLiteralValueId>;
+
+  // Handles parsing `library <name>`. Requires that the position is a `library`
+  // token. Returns the name's ID on success, which may be invalid for
+  // `default`.
+  auto ParseLibrarySpecifier(bool accept_default)
+      -> std::optional<StringLiteralValueId>;
+
   // Sets the package declaration information. Called at most once.
   auto set_packaging_decl(Tree::PackagingNames packaging_names, bool is_impl)
       -> void {
diff --git a/toolchain/parse/handle_decl_scope_loop.cpp b/toolchain/parse/handle_decl_scope_loop.cpp
index 45d899bfc069..95703d4ecaab 100644
--- a/toolchain/parse/handle_decl_scope_loop.cpp
+++ b/toolchain/parse/handle_decl_scope_loop.cpp
@@ -177,6 +177,7 @@ static auto ResolveAmbiguousTokenAsDeclaration(Context& context,
         case Lex::TokenKind::Alias:
         case Lex::TokenKind::Class:
         case Lex::TokenKind::Constraint:
+        case Lex::TokenKind::Extern:
         case Lex::TokenKind::Fn:
         case Lex::TokenKind::Import:
         case Lex::TokenKind::Interface:
@@ -221,6 +222,23 @@ static auto TryHandleAsModifier(Context& context) -> bool {
     return true;
 #include "toolchain/parse/node_kind.def"
 
+    case Lex::TokenKind::Extern: {
+      auto extern_token = context.Consume();
+      if (context.PositionIs(Lex::TokenKind::Library)) {
+        // `extern library <owning_library>` syntax.
+        auto subtree_start = context.tree().size();
+        context.ParseLibrarySpecifier(/*accept_default=*/true);
+        // TODO: Consider error recovery when a non-declaration token is next,
+        // like a typo of the library name.
+        context.AddNode(NodeKind::ExternModifierWithLibrary, extern_token,
+                        subtree_start, /*has_error=*/false);
+      } else {
+        // `extern` syntax without a library.
+        context.AddLeafNode(NodeKind::ExternModifier, extern_token);
+      }
+      return true;
+    }
+
     default:
       return false;
   }
diff --git a/toolchain/parse/handle_import_and_package.cpp b/toolchain/parse/handle_import_and_package.cpp
index 4ccba7b1ad7c..fdb9668ad847 100644
--- a/toolchain/parse/handle_import_and_package.cpp
+++ b/toolchain/parse/handle_import_and_package.cpp
@@ -34,34 +34,6 @@ static auto HasModifier(Context& context, Context::StateStackEntry state,
   return false;
 }
 
-// Handles parsing of the library name. Returns the name's ID on success, which
-// may be invalid for `default`.
-static auto HandleLibraryName(Context& context, bool accept_default)
-    -> std::optional<StringLiteralValueId> {
-  if (auto library_name_token =
-          context.ConsumeIf(Lex::TokenKind::StringLiteral)) {
-    context.AddLeafNode(NodeKind::LibraryName, *library_name_token);
-    return context.tokens().GetStringLiteralValue(*library_name_token);
-  }
-
-  if (accept_default) {
-    if (auto default_token = context.ConsumeIf(Lex::TokenKind::Default)) {
-      context.AddLeafNode(NodeKind::DefaultLibrary, *default_token);
-      return StringLiteralValueId::Invalid;
-    }
-  }
-
-  CARBON_DIAGNOSTIC(
-      ExpectedLibraryNameOrDefault, Error,
-      "Expected `default` or a string literal to specify the library name.");
-  CARBON_DIAGNOSTIC(ExpectedLibraryName, Error,
-                    "Expected a string literal to specify the library name.");
-  context.emitter().Emit(*context.position(), accept_default
-                                                  ? ExpectedLibraryNameOrDefault
-                                                  : ExpectedLibraryName);
-  return std::nullopt;
-}
-
 // Handles everything after the declaration's introducer.
 static auto HandleDeclContent(Context& context, Context::StateStackEntry state,
                               NodeKind declaration, bool is_export,
@@ -102,7 +74,7 @@ static auto HandleDeclContent(Context& context, Context::StateStackEntry state,
   // Parse the optional library keyword.
   bool accept_default = !names.package_id.is_valid();
   if (declaration == NodeKind::LibraryDecl) {
-    auto library_id = HandleLibraryName(context, accept_default);
+    auto library_id = context.ParseLibraryName(accept_default);
     if (!library_id) {
       on_parse_error();
       return;
@@ -111,17 +83,12 @@ static auto HandleDeclContent(Context& context, Context::StateStackEntry state,
   } else {
     auto next_kind = context.PositionKind();
     if (next_kind == Lex::TokenKind::Library) {
-      auto library_token = context.ConsumeChecked(Lex::TokenKind::Library);
-      auto library_subtree_start = context.tree().size();
-      auto library_id = HandleLibraryName(context, accept_default);
-      if (!library_id) {
+      if (auto library_id = context.ParseLibrarySpecifier(accept_default)) {
+        names.library_id = *library_id;
+      } else {
         on_parse_error();
         return;
       }
-      names.library_id = *library_id;
-      context.AddNode(NodeKind::LibrarySpecifier, library_token,
-                      library_subtree_start,
-                      /*has_error=*/false);
     } else if (next_kind == Lex::TokenKind::StringLiteral ||
                (accept_default && next_kind == Lex::TokenKind::Default)) {
       // If we come across a string literal and we didn't parse `library
diff --git a/toolchain/parse/node_kind.def b/toolchain/parse/node_kind.def
index 097daaf68ca8..b03228f9b585 100644
--- a/toolchain/parse/node_kind.def
+++ b/toolchain/parse/node_kind.def
@@ -286,12 +286,14 @@ CARBON_PARSE_NODE_KIND(StructComma)
 CARBON_PARSE_NODE_KIND(StructLiteral)
 CARBON_PARSE_NODE_KIND(StructTypeLiteral)
 
+CARBON_PARSE_NODE_KIND(ExternModifierWithLibrary)
+CARBON_PARSE_NODE_KIND(ExternModifier)
+
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Abstract)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Base)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Default)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Export)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Extend)
-CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Extern)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Final)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Impl)
 CARBON_PARSE_NODE_KIND_TOKEN_MODIFIER(Private)
diff --git a/toolchain/parse/testdata/function/declaration/basic.carbon b/toolchain/parse/testdata/function/declaration/basic.carbon
index 38a051f9355a..42aaefbd458a 100644
--- a/toolchain/parse/testdata/function/declaration/basic.carbon
+++ b/toolchain/parse/testdata/function/declaration/basic.carbon
@@ -9,7 +9,6 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/function/declaration/basic.carbon
 
 fn F();
-extern fn G();
 
 // CHECK:STDOUT: - filename: basic.carbon
 // CHECK:STDOUT:   parse_tree: [
@@ -19,11 +18,5 @@ extern fn G();
 // CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
 // CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
 // CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 5},
-// CHECK:STDOUT:       {kind: 'FunctionIntroducer', text: 'fn'},
-// CHECK:STDOUT:       {kind: 'ExternModifier', text: 'extern'},
-// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'G'},
-// CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
-// CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
-// CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 6},
 // CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT:   ]
diff --git a/toolchain/parse/testdata/function/declaration/extern.carbon b/toolchain/parse/testdata/function/declaration/extern.carbon
new file mode 100644
index 000000000000..4e9ebcab0966
--- /dev/null
+++ b/toolchain/parse/testdata/function/declaration/extern.carbon
@@ -0,0 +1,101 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/function/declaration/extern.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/function/declaration/extern.carbon
+
+// --- extern.carbon
+
+extern fn G();
+
+// --- library.carbon
+
+extern library "foo" fn G();
+
+// --- default_library.carbon
+
+extern library default fn G();
+
+// --- fail_name_missing.carbon
+
+// CHECK:STDERR: fail_name_missing.carbon:[[@LINE+4]]:16: ERROR: Expected `default` or a string literal to specify the library name.
+// CHECK:STDERR: extern library fn G();
+// CHECK:STDERR:                ^~
+// CHECK:STDERR:
+extern library fn G();
+
+// --- fail_identifier.carbon
+
+// CHECK:STDERR: fail_identifier.carbon:[[@LINE+7]]:16: ERROR: Expected `default` or a string literal to specify the library name.
+// CHECK:STDERR: extern library foo fn G();
+// CHECK:STDERR:                ^~~
+// CHECK:STDERR:
+// CHECK:STDERR: fail_identifier.carbon:[[@LINE+3]]:16: ERROR: Unrecognized declaration introducer.
+// CHECK:STDERR: extern library foo fn G();
+// CHECK:STDERR:                ^~~
+extern library foo fn G();
+
+// CHECK:STDOUT: - filename: extern.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:       {kind: 'ExternModifier', text: 'extern'},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 6},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
+// CHECK:STDOUT: - filename: library.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:           {kind: 'LibraryName', text: '"foo"'},
+// CHECK:STDOUT:         {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'ExternModifierWithLibrary', text: 'extern', subtree_size: 3},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 8},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
+// CHECK:STDOUT: - filename: default_library.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:           {kind: 'DefaultLibrary', text: 'default'},
+// CHECK:STDOUT:         {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'ExternModifierWithLibrary', text: 'extern', subtree_size: 3},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 8},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
+// CHECK:STDOUT: - filename: fail_name_missing.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:           {kind: 'LibraryName', text: 'fn', has_error: yes},
+// CHECK:STDOUT:         {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'ExternModifierWithLibrary', text: 'extern', subtree_size: 3},
+// CHECK:STDOUT:       {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:         {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:       {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'FunctionDecl', text: ';', subtree_size: 8},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
+// CHECK:STDOUT: - filename: fail_identifier.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'InvalidParseStart', text: 'foo', has_error: yes},
+// CHECK:STDOUT:           {kind: 'LibraryName', text: 'foo', has_error: yes},
+// CHECK:STDOUT:         {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'ExternModifierWithLibrary', text: 'extern', subtree_size: 3},
+// CHECK:STDOUT:     {kind: 'InvalidParseSubtree', text: ';', has_error: yes, subtree_size: 5},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
diff --git a/toolchain/parse/testdata/function/definition/basic.carbon b/toolchain/parse/testdata/function/definition/basic.carbon
index d4c42806db0c..135d9643022c 100644
--- a/toolchain/parse/testdata/function/definition/basic.carbon
+++ b/toolchain/parse/testdata/function/definition/basic.carbon
@@ -9,7 +9,6 @@
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/function/definition/basic.carbon
 
 fn F() {}
-extern fn G() {}
 
 // CHECK:STDOUT: - filename: basic.carbon
 // CHECK:STDOUT:   parse_tree: [
@@ -20,12 +19,5 @@ extern fn G() {}
 // CHECK:STDOUT:         {kind: 'TuplePattern', text: ')', subtree_size: 2},
 // CHECK:STDOUT:       {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
 // CHECK:STDOUT:     {kind: 'FunctionDefinition', text: '}', subtree_size: 6},
-// CHECK:STDOUT:         {kind: 'FunctionIntroducer', text: 'fn'},
-// CHECK:STDOUT:         {kind: 'ExternModifier', text: 'extern'},
-// CHECK:STDOUT:         {kind: 'IdentifierName', text: 'G'},
-// CHECK:STDOUT:           {kind: 'TuplePatternStart', text: '('},
-// CHECK:STDOUT:         {kind: 'TuplePattern', text: ')', subtree_size: 2},
-// CHECK:STDOUT:       {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 6},
-// CHECK:STDOUT:     {kind: 'FunctionDefinition', text: '}', subtree_size: 7},
 // CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT:   ]
diff --git a/toolchain/parse/testdata/function/definition/extern.carbon b/toolchain/parse/testdata/function/definition/extern.carbon
new file mode 100644
index 000000000000..3e93334769fe
--- /dev/null
+++ b/toolchain/parse/testdata/function/definition/extern.carbon
@@ -0,0 +1,44 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/function/definition/extern.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/function/definition/extern.carbon
+
+// --- extern.carbon
+
+extern fn G() {}
+
+// --- library.carbon
+
+extern library "foo" fn G() {}
+
+// CHECK:STDOUT: - filename: extern.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:         {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:         {kind: 'ExternModifier', text: 'extern'},
+// CHECK:STDOUT:         {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:           {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:         {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 6},
+// CHECK:STDOUT:     {kind: 'FunctionDefinition', text: '}', subtree_size: 7},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
+// CHECK:STDOUT: - filename: library.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:         {kind: 'FunctionIntroducer', text: 'fn'},
+// CHECK:STDOUT:             {kind: 'LibraryName', text: '"foo"'},
+// CHECK:STDOUT:           {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:         {kind: 'ExternModifierWithLibrary', text: 'extern', subtree_size: 3},
+// CHECK:STDOUT:         {kind: 'IdentifierName', text: 'G'},
+// CHECK:STDOUT:           {kind: 'TuplePatternStart', text: '('},
+// CHECK:STDOUT:         {kind: 'TuplePattern', text: ')', subtree_size: 2},
+// CHECK:STDOUT:       {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 8},
+// CHECK:STDOUT:     {kind: 'FunctionDefinition', text: '}', subtree_size: 9},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]
diff --git a/toolchain/parse/testdata/packages/import/fail_library_is_identifier.carbon b/toolchain/parse/testdata/packages/import/fail_library_is_identifier.carbon
index 417044a989eb..de2d019caa76 100644
--- a/toolchain/parse/testdata/packages/import/fail_library_is_identifier.carbon
+++ b/toolchain/parse/testdata/packages/import/fail_library_is_identifier.carbon
@@ -18,6 +18,8 @@ import Geometry library Shapes;
 // CHECK:STDOUT:     {kind: 'FileStart', text: ''},
 // CHECK:STDOUT:       {kind: 'ImportIntroducer', text: 'import'},
 // CHECK:STDOUT:       {kind: 'PackageName', text: 'Geometry'},
-// CHECK:STDOUT:     {kind: 'ImportDecl', text: ';', has_error: yes, subtree_size: 3},
+// CHECK:STDOUT:         {kind: 'LibraryName', text: 'Shapes', has_error: yes},
+// CHECK:STDOUT:       {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'ImportDecl', text: ';', has_error: yes, subtree_size: 5},
 // CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT:   ]
diff --git a/toolchain/parse/testdata/packages/package/fail_library_is_identifier.carbon b/toolchain/parse/testdata/packages/package/fail_library_is_identifier.carbon
index 400ddf136819..456d5c68ea73 100644
--- a/toolchain/parse/testdata/packages/package/fail_library_is_identifier.carbon
+++ b/toolchain/parse/testdata/packages/package/fail_library_is_identifier.carbon
@@ -18,6 +18,8 @@ package Geometry library Shapes;
 // CHECK:STDOUT:     {kind: 'FileStart', text: ''},
 // CHECK:STDOUT:       {kind: 'PackageIntroducer', text: 'package'},
 // CHECK:STDOUT:       {kind: 'PackageName', text: 'Geometry'},
-// CHECK:STDOUT:     {kind: 'PackageDecl', text: ';', has_error: yes, subtree_size: 3},
+// CHECK:STDOUT:         {kind: 'LibraryName', text: 'Shapes', has_error: yes},
+// CHECK:STDOUT:       {kind: 'LibrarySpecifier', text: 'library', subtree_size: 2},
+// CHECK:STDOUT:     {kind: 'PackageDecl', text: ';', has_error: yes, subtree_size: 5},
 // CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT:   ]
diff --git a/toolchain/parse/typed_nodes.h b/toolchain/parse/typed_nodes.h
index 41a342e3bc81..00d70512d629 100644
--- a/toolchain/parse/typed_nodes.h
+++ b/toolchain/parse/typed_nodes.h
@@ -924,6 +924,19 @@ struct PostfixOperator {
       PostfixOperator<NodeKind::PostfixOperator##Name, Lex::Name##TokenIndex>;
 #include "toolchain/parse/node_kind.def"
 
+// `extern` as a standalone modifier.
+using ExternModifier = LeafNode<NodeKind::ExternModifier, Lex::ExternTokenIndex,
+                                NodeCategory::Modifier>;
+
+// `extern library <owning_library>` modifiers.
+struct ExternModifierWithLibrary {
+  static constexpr auto Kind = NodeKind::ExternModifierWithLibrary.Define(
+      {.category = NodeCategory::Modifier, .child_count = 1});
+
+  Lex::ExternTokenIndex token;
+  LibrarySpecifierId library;
+};
+
 // The first operand of a short-circuiting infix operator: `a and` or `a or`.
 // The complete operator expression will be an InfixOperator with this as the
 // `lhs`.