diff --git a/BUILD b/BUILD
index cd515ba430..43de536048 100644
--- a/BUILD
+++ b/BUILD
@@ -326,15 +326,31 @@ cc_library(
 
 cc_library(
     name = "generated_reflection_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
+    srcs = [
+        "upb/reflection/common.h",
+        "upb/reflection/def_pool.h",
+        "upb/reflection/def_type.h",
+        "upb/reflection/enum_def.h",
+        "upb/reflection/enum_value_def.h",
+        "upb/reflection/extension_range.h",
+        "upb/reflection/field_def.h",
+        "upb/reflection/file_def.h",
+        "upb/reflection/message_def.h",
+        "upb/reflection/method_def.h",
+        "upb/reflection/oneof_def.h",
+        "upb/reflection/service_def.h",
+    ],
     hdrs = [
-        "upb/def.h",
         "upb/port_def.inc",
         "upb/port_undef.inc",
+        "upb/reflection/def.h",
     ],
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//visibility:public"],
     deps = [
+        ":descriptor_upb_proto",
         ":reflection",
+        ":table_internal",
     ],
 )
 
diff --git a/benchmarks/benchmark.cc b/benchmarks/benchmark.cc
index e752d3e7eb..e4c3a0cba1 100644
--- a/benchmarks/benchmark.cc
+++ b/benchmarks/benchmark.cc
@@ -35,7 +35,7 @@
 #include "benchmarks/descriptor.upb.h"
 #include "benchmarks/descriptor.upbdefs.h"
 #include "benchmarks/descriptor_sv.pb.h"
-#include "upb/def.hpp"
+#include "upb/reflection/def.hpp"
 
 upb_StringView descriptor = benchmarks_descriptor_proto_upbdefinit.descriptor;
 namespace protobuf = ::google::protobuf;
diff --git a/python/convert.c b/python/convert.c
index b9df5019a1..b079bdcbf7 100644
--- a/python/convert.c
+++ b/python/convert.c
@@ -30,7 +30,7 @@
 #include "python/message.h"
 #include "python/protobuf.h"
 #include "upb/map.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 #include "upb/util/compare.h"
 
 // Must be last.
diff --git a/python/convert.h b/python/convert.h
index d26aeb72a5..c02c1976a3 100644
--- a/python/convert.h
+++ b/python/convert.h
@@ -29,8 +29,8 @@
 #define PYUPB_CONVERT_H__
 
 #include "protobuf.h"
-#include "upb/def.h"
-#include "upb/reflection.h"
+#include "upb/reflection/def.h"
+#include "upb/reflection/message.h"
 
 // Converts `val` to a Python object according to the type information in `f`.
 // Any newly-created Python objects that reference non-primitive data from `val`
diff --git a/python/descriptor.c b/python/descriptor.c
index 4d238bc4b8..5e3a5fdfd6 100644
--- a/python/descriptor.c
+++ b/python/descriptor.c
@@ -32,7 +32,7 @@
 #include "python/descriptor_pool.h"
 #include "python/message.h"
 #include "python/protobuf.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 #include "upb/util/def_to_proto.h"
 
 // -----------------------------------------------------------------------------
diff --git a/python/descriptor.h b/python/descriptor.h
index b4229ef616..9bf6b4258d 100644
--- a/python/descriptor.h
+++ b/python/descriptor.h
@@ -31,7 +31,7 @@
 #include <stdbool.h>
 
 #include "python/python_api.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 typedef enum {
   kPyUpb_Descriptor = 0,
diff --git a/python/descriptor_containers.c b/python/descriptor_containers.c
index 0f2d4ff023..c750a4a04f 100644
--- a/python/descriptor_containers.c
+++ b/python/descriptor_containers.c
@@ -29,7 +29,7 @@
 
 #include "python/descriptor.h"
 #include "python/protobuf.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Implements __repr__ as str(dict(self)).
 static PyObject* PyUpb_DescriptorMap_Repr(PyObject* _self) {
diff --git a/python/descriptor_containers.h b/python/descriptor_containers.h
index 8c6b0d9b43..276aea558a 100644
--- a/python/descriptor_containers.h
+++ b/python/descriptor_containers.h
@@ -43,7 +43,7 @@
 #include <stdbool.h>
 
 #include "protobuf.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // -----------------------------------------------------------------------------
 // PyUpb_GenericSequence
diff --git a/python/descriptor_pool.c b/python/descriptor_pool.c
index ea0e8132a6..4e9faaad2f 100644
--- a/python/descriptor_pool.c
+++ b/python/descriptor_pool.c
@@ -32,7 +32,7 @@
 #include "python/descriptor.h"
 #include "python/message.h"
 #include "python/protobuf.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 #include "upb/util/def_to_proto.h"
 
 // -----------------------------------------------------------------------------
diff --git a/python/map.c b/python/map.c
index c5c6e68309..dfadf41d82 100644
--- a/python/map.c
+++ b/python/map.c
@@ -30,8 +30,8 @@
 #include "python/convert.h"
 #include "python/message.h"
 #include "python/protobuf.h"
-#include "upb/def.h"
 #include "upb/map.h"
+#include "upb/reflection/def.h"
 
 // -----------------------------------------------------------------------------
 // MapContainer
diff --git a/python/map.h b/python/map.h
index aaa4e20385..e69ff9fe28 100644
--- a/python/map.h
+++ b/python/map.h
@@ -31,7 +31,7 @@
 #include <stdbool.h>
 
 #include "python/python_api.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Creates a new repeated field stub for field `f` of message object `parent`.
 // Precondition: `parent` must be a stub.
diff --git a/python/message.c b/python/message.c
index e67bf2306b..175292280e 100644
--- a/python/message.c
+++ b/python/message.c
@@ -32,8 +32,8 @@
 #include "python/extension_dict.h"
 #include "python/map.h"
 #include "python/repeated.h"
-#include "upb/def.h"
-#include "upb/reflection.h"
+#include "upb/reflection/def.h"
+#include "upb/reflection/message.h"
 #include "upb/text_encode.h"
 #include "upb/util/required_fields.h"
 
diff --git a/python/message.h b/python/message.h
index f296d5ce93..f10f15f02a 100644
--- a/python/message.h
+++ b/python/message.h
@@ -31,7 +31,7 @@
 #include <stdbool.h>
 
 #include "python/protobuf.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 // Removes the wrapper object for this field from the unset subobject cache.
 void PyUpb_Message_CacheDelete(PyObject* _self, const upb_FieldDef* f);
diff --git a/python/repeated.h b/python/repeated.h
index 5d74bd2edb..8cd38721a5 100644
--- a/python/repeated.h
+++ b/python/repeated.h
@@ -31,7 +31,7 @@
 #include <stdbool.h>
 
 #include "python/python_api.h"
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Creates a new repeated field stub for field `f` of message object `parent`.
 // Precondition: `parent` must be a stub.
diff --git a/upb/bindings/lua/def.c b/upb/bindings/lua/def.c
index 602dbaf9a4..b28ed42cb2 100644
--- a/upb/bindings/lua/def.c
+++ b/upb/bindings/lua/def.c
@@ -25,7 +25,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 #include <float.h>
 #include <math.h>
diff --git a/upb/bindings/lua/msg.c b/upb/bindings/lua/msg.c
index 9c66c74b04..4e37e0cecc 100644
--- a/upb/bindings/lua/msg.c
+++ b/upb/bindings/lua/msg.c
@@ -43,7 +43,7 @@
 #include "upb/json_encode.h"
 #include "upb/map.h"
 #include "upb/port_def.inc"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 #include "upb/text_encode.h"
 
 /*
diff --git a/upb/bindings/lua/upb.h b/upb/bindings/lua/upb.h
index e0dc79eb04..a06d964d55 100644
--- a/upb/bindings/lua/upb.h
+++ b/upb/bindings/lua/upb.h
@@ -33,9 +33,9 @@
 #define UPB_LUA_UPB_H_
 
 #include "lauxlib.h"
-#include "upb/def.h"
 #include "upb/msg.h"
-#include "upb/reflection.h"
+#include "upb/reflection/def.h"
+#include "upb/reflection/message.h"
 
 /* Lua changes its API in incompatible ways in every minor release.
  * This is some shim code to paper over the differences. */
diff --git a/upb/conformance_upb.c b/upb/conformance_upb.c
index be5ce9c7dc..b08239b6ff 100644
--- a/upb/conformance_upb.c
+++ b/upb/conformance_upb.c
@@ -43,7 +43,7 @@
 #include "upb/encode.h"
 #include "upb/json_decode.h"
 #include "upb/json_encode.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 #include "upb/text_encode.h"
 
 // Must be last.
diff --git a/upb/json_decode.c b/upb/json_decode.c
index 56775cb778..2342d688e1 100644
--- a/upb/json_decode.c
+++ b/upb/json_decode.c
@@ -39,7 +39,7 @@
 #include "upb/internal/atoi.h"
 #include "upb/internal/unicode.h"
 #include "upb/map.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/json_decode.h b/upb/json_decode.h
index c7b6839427..a5abad279f 100644
--- a/upb/json_decode.h
+++ b/upb/json_decode.h
@@ -28,7 +28,7 @@
 #ifndef UPB_JSONDECODE_H_
 #define UPB_JSONDECODE_H_
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/json_decode_test.cc b/upb/json_decode_test.cc
index fcc65a9360..2d41e602d8 100644
--- a/upb/json_decode_test.cc
+++ b/upb/json_decode_test.cc
@@ -31,9 +31,9 @@
 
 #include "google/protobuf/struct.upb.h"
 #include "gtest/gtest.h"
-#include "upb/def.hpp"
 #include "upb/json_test.upb.h"
 #include "upb/json_test.upbdefs.h"
+#include "upb/reflection/def.hpp"
 #include "upb/upb.hpp"
 
 static upb_test_Box* JsonDecode(const char* json, upb_Arena* a) {
diff --git a/upb/json_encode.c b/upb/json_encode.c
index 9c657dddcd..487ee11098 100644
--- a/upb/json_encode.c
+++ b/upb/json_encode.c
@@ -39,7 +39,7 @@
 #include "upb/internal/encode.h"
 #include "upb/internal/vsnprintf_compat.h"
 #include "upb/map.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/json_encode.h b/upb/json_encode.h
index 7d83206580..b2207a9807 100644
--- a/upb/json_encode.h
+++ b/upb/json_encode.h
@@ -28,7 +28,7 @@
 #ifndef UPB_JSONENCODE_H_
 #define UPB_JSONENCODE_H_
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/json_encode_test.cc b/upb/json_encode_test.cc
index 7abd23a93b..0d14b4176d 100644
--- a/upb/json_encode_test.cc
+++ b/upb/json_encode_test.cc
@@ -25,12 +25,13 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "upb/json_encode.h"
+
 #include "google/protobuf/struct.upb.h"
 #include "gtest/gtest.h"
-#include "upb/def.hpp"
-#include "upb/json_encode.h"
 #include "upb/json_test.upb.h"
 #include "upb/json_test.upbdefs.h"
+#include "upb/reflection/def.hpp"
 #include "upb/upb.hpp"
 
 static std::string JsonEncode(const upb_test_Box* msg, int options) {
diff --git a/upb/msg_test.cc b/upb/msg_test.cc
index 9e1548ae9d..113972321a 100644
--- a/upb/msg_test.cc
+++ b/upb/msg_test.cc
@@ -28,12 +28,12 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "google/protobuf/test_messages_proto3.upb.h"
-#include "upb/def.hpp"
 #include "upb/fuzz_test_util.h"
 #include "upb/json_decode.h"
 #include "upb/json_encode.h"
 #include "upb/msg_test.upb.h"
 #include "upb/msg_test.upbdefs.h"
+#include "upb/reflection/def.hpp"
 #include "upb/upb.hpp"
 
 // begin:google_only
diff --git a/upb/test_cpp.cc b/upb/test_cpp.cc
index 4d4aec6253..e70771420b 100644
--- a/upb/test_cpp.cc
+++ b/upb/test_cpp.cc
@@ -38,10 +38,10 @@
 #include "google/protobuf/timestamp.upb.h"
 #include "google/protobuf/timestamp.upbdefs.h"
 #include "gtest/gtest.h"
-#include "upb/def.h"
-#include "upb/def.hpp"
 #include "upb/json_decode.h"
 #include "upb/json_encode.h"
+#include "upb/reflection/def.h"
+#include "upb/reflection/def.hpp"
 #include "upb/test_cpp.upb.h"
 #include "upb/test_cpp.upbdefs.h"
 #include "upb/upb.h"
diff --git a/upb/text_encode.c b/upb/text_encode.c
index 393b8d7615..d3e9f0145c 100644
--- a/upb/text_encode.c
+++ b/upb/text_encode.c
@@ -37,7 +37,7 @@
 #include "upb/internal/encode.h"
 #include "upb/internal/vsnprintf_compat.h"
 #include "upb/map.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/text_encode.h b/upb/text_encode.h
index 312db24e35..30f7404c80 100644
--- a/upb/text_encode.h
+++ b/upb/text_encode.h
@@ -28,7 +28,7 @@
 #ifndef UPB_TEXTENCODE_H_
 #define UPB_TEXTENCODE_H_
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/util/compare.h b/upb/util/compare.h
index 92f6d83ab7..d99a7e956b 100644
--- a/upb/util/compare.h
+++ b/upb/util/compare.h
@@ -28,7 +28,7 @@
 #ifndef UPB_UTIL_COMPARE_H_
 #define UPB_UTIL_COMPARE_H_
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/upb/util/def_to_proto.c b/upb/util/def_to_proto.c
index ae9288c9e0..ab957db578 100644
--- a/upb/util/def_to_proto.c
+++ b/upb/util/def_to_proto.c
@@ -33,7 +33,7 @@
 #include <stdio.h>
 
 #include "upb/internal/vsnprintf_compat.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 /* Must be last. */
 #include "upb/port_def.inc"
diff --git a/upb/util/def_to_proto.h b/upb/util/def_to_proto.h
index 24f65b9bfb..08c64532e9 100644
--- a/upb/util/def_to_proto.h
+++ b/upb/util/def_to_proto.h
@@ -28,7 +28,7 @@
 #ifndef UPB_UTIL_DEF_TO_PROTO_H_
 #define UPB_UTIL_DEF_TO_PROTO_H_
 
-#include "upb/def.h"
+#include "upb/reflection/def.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/upb/util/def_to_proto_test.cc b/upb/util/def_to_proto_test.cc
index d8156e3989..b83e1c3623 100644
--- a/upb/util/def_to_proto_test.cc
+++ b/upb/util/def_to_proto_test.cc
@@ -27,13 +27,13 @@
 
 #include "upb/util/def_to_proto.h"
 
-#include "gmock/gmock.h"
 #include "google/protobuf/descriptor.pb.h"
 #include "google/protobuf/descriptor.upbdefs.h"
 #include "google/protobuf/dynamic_message.h"
 #include "google/protobuf/util/message_differencer.h"
+#include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include "upb/def.hpp"
+#include "upb/reflection/def.hpp"
 #include "upb/upb.hpp"
 #include "upb/util/def_to_proto_test.upbdefs.h"
 
diff --git a/upb/util/required_fields.c b/upb/util/required_fields.c
index 260a5b1d09..2bc714509d 100644
--- a/upb/util/required_fields.c
+++ b/upb/util/required_fields.c
@@ -34,7 +34,7 @@
 
 #include "upb/internal/vsnprintf_compat.h"
 #include "upb/map.h"
-#include "upb/reflection.h"
+#include "upb/reflection/message.h"
 
 // Must be last.
 #include "upb/port_def.inc"
diff --git a/upb/util/required_fields.h b/upb/util/required_fields.h
index 874914bd67..e58f7ca38f 100644
--- a/upb/util/required_fields.h
+++ b/upb/util/required_fields.h
@@ -28,8 +28,8 @@
 #ifndef UPB_UTIL_REQUIRED_FIELDS_H_
 #define UPB_UTIL_REQUIRED_FIELDS_H_
 
-#include "upb/def.h"
-#include "upb/reflection.h"
+#include "upb/reflection/def.h"
+#include "upb/reflection/message.h"
 
 /* Must be last. */
 #include "upb/port_def.inc"
diff --git a/upb/util/required_fields_test.cc b/upb/util/required_fields_test.cc
index 85504101e6..7d44ef7954 100644
--- a/upb/util/required_fields_test.cc
+++ b/upb/util/required_fields_test.cc
@@ -27,11 +27,11 @@
 
 #include "upb/util/required_fields.h"
 
-#include "absl/strings/string_view.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include "upb/def.hpp"
+#include "absl/strings/string_view.h"
 #include "upb/json_decode.h"
+#include "upb/reflection/def.hpp"
 #include "upb/upb.hpp"
 #include "upb/util/required_fields_test.upb.h"
 #include "upb/util/required_fields_test.upbdefs.h"
diff --git a/upbc/protoc-gen-upbdefs.cc b/upbc/protoc-gen-upbdefs.cc
index 51b3b95927..e1924218d4 100644
--- a/upbc/protoc-gen-upbdefs.cc
+++ b/upbc/protoc-gen-upbdefs.cc
@@ -69,14 +69,14 @@ void WriteDefHeader(const protobuf::FileDescriptor* file, Output& output) {
   output(
       "#ifndef $0_UPBDEFS_H_\n"
       "#define $0_UPBDEFS_H_\n\n"
-      "#include \"upb/def.h\"\n"
+      "#include \"upb/reflection/def.h\"\n"
       "#include \"upb/port_def.inc\"\n"
       "#ifdef __cplusplus\n"
       "extern \"C\" {\n"
       "#endif\n\n",
       ToPreproc(file->name()));
 
-  output("#include \"upb/def.h\"\n");
+  output("#include \"upb/reflection/def.h\"\n");
   output("\n");
   output("#include \"upb/port_def.inc\"\n");
   output("\n");
@@ -102,7 +102,7 @@ void WriteDefHeader(const protobuf::FileDescriptor* file, Output& output) {
 void WriteDefSource(const protobuf::FileDescriptor* file, Output& output) {
   EmitFileWarning(file, output);
 
-  output("#include \"upb/def.h\"\n");
+  output("#include \"upb/reflection/def.h\"\n");
   output("#include \"$0\"\n", DefHeaderFilename(file->name()));
   output("#include \"$0\"\n", HeaderFilename(file));
   output("\n");