diff --git a/.github/workflows/test_upb.yml b/.github/workflows/test_upb.yml
index 21ec308876..f2c1cfa2e4 100644
--- a/.github/workflows/test_upb.yml
+++ b/.github/workflows/test_upb.yml
@@ -76,7 +76,7 @@ jobs:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           bazel-cache: "upb-bazel-windows"
           bazel: test --cxxopt=/std:c++17 --host_cxxopt=/std:c++17 //upb/... //upb_generator/... //python/... //protos/... //protos_generator/...
-          exclude-targets: -//python:conformance_test -//upb:def_builder_test
+          exclude-targets: -//python:conformance_test -//upb/reflection:def_builder_test
 
   macos:
     strategy:
diff --git a/upb/BUILD b/upb/BUILD
index 02d65bdee2..16c67b17e0 100644
--- a/upb/BUILD
+++ b/upb/BUILD
@@ -8,14 +8,7 @@
 load("@rules_python//python:defs.bzl", "py_binary")
 load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 load("//bazel:build_defs.bzl", "UPB_DEFAULT_COPTS")
-load("//bazel:upb_minitable_proto_library.bzl", "upb_minitable_proto_library")
-load("//bazel:upb_proto_library.bzl", "upb_proto_reflection_library")
 load("//bazel:upb_proto_library_internal/copts.bzl", "upb_proto_library_copts")
-load(
-    "//upb_generator:bootstrap_compiler.bzl",
-    "bootstrap_cc_library",
-    "bootstrap_upb_proto_library",
-)
 
 # begin:google_only
 # load("//tools/build_defs/kotlin/native:rules.bzl", "kt_native_interop_hint")
@@ -111,7 +104,7 @@ cc_library(
     hdrs = ["generated_code_support.h"],
     copts = UPB_DEFAULT_COPTS,
     textual_hdrs = [
-        "//upb/port:inc",
+        ":port_inc",
     ],
     visibility = ["//visibility:public"],
     deps = [
@@ -133,176 +126,54 @@ cc_library(
     name = "generated_cpp_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
     copts = UPB_DEFAULT_COPTS,
     textual_hdrs = [
-        "//upb/port:inc",
+        ":port_inc",
     ],
     visibility = ["//visibility:public"],
 )
 
-cc_library(
-    name = "generated_reflection_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
-    hdrs = [
-        "reflection/def.h",
-        "reflection/internal/def_pool.h",
-    ],
-    copts = UPB_DEFAULT_COPTS,
-    textual_hdrs = [
-        "//upb/port:inc",
-    ],
-    visibility = ["//visibility:public"],
-    deps = [
-        ":mem",
-        ":mini_descriptor",
-        ":reflection_internal",
-    ],
-)
+# Aliases ######################################################################
+# TODO: Remove these.
 
-bootstrap_upb_proto_library(
-    name = "descriptor_upb_proto",
-    base_dir = "reflection/",
-    # TODO: Export 'net/proto2/proto/descriptor.upb.h' and remove "-layering_check".
-    features = ["-layering_check"],
-    google3_src_files = ["net/proto2/proto/descriptor.proto"],
-    google3_src_rules = ["//net/proto2/proto:descriptor_proto_source"],
-    oss_src_files = ["google/protobuf/descriptor.proto"],
-    oss_src_rules = ["//:descriptor_proto_srcs"],
-    oss_strip_prefix = "third_party/protobuf/github/bootstrap/src",
-    proto_lib_deps = ["//:descriptor_proto"],
+alias(
+    name = "base",
+    actual = "//upb/base",
     visibility = ["//visibility:public"],
 )
 
-upb_proto_reflection_library(
-    name = "descriptor_upb_proto_reflection",
+alias(
+    name = "base_internal",
+    actual = "//upb/base:internal",
     visibility = ["//visibility:public"],
-    deps = ["//:descriptor_proto"],
 )
 
-upb_minitable_proto_library(
-    name = "descriptor_upb_minitable_proto",
-    visibility = [
-        "//upb:__subpackages__",
-        # begin:github_only
-        "//python:__subpackages__",
-        # end:github_only
-    ],
-    deps = ["//:descriptor_proto"],
-)
-
-# TODO: Once we can delete the deprecated forwarding headers
-# (= everything in upb/) we can move this build target down into reflection/
-bootstrap_cc_library(
-    name = "reflection",
-    hdrs = [
-        "reflection/def.h",
-        "reflection/def.hpp",
-        "reflection/message.h",
-        "reflection/message.hpp",
-    ],
-    bootstrap_deps = [":reflection_internal"],
-    copts = UPB_DEFAULT_COPTS,
+alias(
+    name = "collections",
+    actual = "//upb/collections",
+    deprecation = "use upb:message instead",
     visibility = ["//visibility:public"],
-    deps = [
-        ":base",
-        ":mem",
-        ":message",
-        ":message_types",
-        ":message_value",
-        ":port",
-    ],
 )
 
-bootstrap_cc_library(
-    name = "reflection_internal",
-    srcs = [
-        "reflection/def_pool.c",
-        "reflection/def_type.c",
-        "reflection/desc_state.c",
-        "reflection/enum_def.c",
-        "reflection/enum_reserved_range.c",
-        "reflection/enum_value_def.c",
-        "reflection/extension_range.c",
-        "reflection/field_def.c",
-        "reflection/file_def.c",
-        "reflection/internal/def_builder.c",
-        "reflection/internal/def_builder.h",
-        "reflection/internal/strdup2.c",
-        "reflection/internal/strdup2.h",
-        "reflection/message.c",
-        "reflection/message_def.c",
-        "reflection/message_reserved_range.c",
-        "reflection/method_def.c",
-        "reflection/oneof_def.c",
-        "reflection/service_def.c",
-    ],
-    hdrs = [
-        "reflection/common.h",
-        "reflection/def.h",
-        "reflection/def.hpp",
-        "reflection/def_pool.h",
-        "reflection/def_type.h",
-        "reflection/enum_def.h",
-        "reflection/enum_reserved_range.h",
-        "reflection/enum_value_def.h",
-        "reflection/extension_range.h",
-        "reflection/field_def.h",
-        "reflection/file_def.h",
-        "reflection/internal/def_pool.h",
-        "reflection/internal/desc_state.h",
-        "reflection/internal/enum_def.h",
-        "reflection/internal/enum_reserved_range.h",
-        "reflection/internal/enum_value_def.h",
-        "reflection/internal/extension_range.h",
-        "reflection/internal/field_def.h",
-        "reflection/internal/file_def.h",
-        "reflection/internal/message_def.h",
-        "reflection/internal/message_reserved_range.h",
-        "reflection/internal/method_def.h",
-        "reflection/internal/oneof_def.h",
-        "reflection/internal/service_def.h",
-        "reflection/message.h",
-        "reflection/message.hpp",
-        "reflection/message_def.h",
-        "reflection/message_reserved_range.h",
-        "reflection/method_def.h",
-        "reflection/oneof_def.h",
-        "reflection/service_def.h",
-    ],
-    bootstrap_deps = [":descriptor_upb_proto"],
-    copts = UPB_DEFAULT_COPTS,
+alias(
+    name = "descriptor_upb_proto",
+    actual = "//upb/reflection:descriptor_upb_proto",
     visibility = ["//visibility:public"],
-    deps = [
-        ":base",
-        ":hash",
-        ":mem",
-        ":message",
-        ":message_accessors",
-        ":message_types",
-        ":message_value",
-        ":mini_descriptor",
-        ":mini_descriptor_internal",
-        ":mini_table",
-        ":port",
-    ],
 )
 
-# Aliases ######################################################################
-# TODO: Remove these.
-
 alias(
-    name = "base",
-    actual = "//upb/base",
+    name = "descriptor_upb_minitable_proto",
+    actual = "//upb/reflection:descriptor_upb_minitable_proto",
     visibility = ["//visibility:public"],
 )
 
 alias(
-    name = "base_internal",
-    actual = "//upb/base:internal",
+    name = "descriptor_upb_proto_reflection",
+    actual = "//upb/reflection:descriptor_upb_proto_reflection",
     visibility = ["//visibility:public"],
 )
 
 alias(
-    name = "collections",
-    actual = "//upb/collections",
-    deprecation = "use upb:message instead",
+    name = "generated_reflection_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
+    actual = "//upb/reflection:generated_reflection_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
     visibility = ["//visibility:public"],
 )
 
@@ -438,6 +309,24 @@ alias(
     visibility = ["//visibility:public"],
 )
 
+alias(
+    name = "port_inc",
+    actual = "//upb/port:inc",
+    visibility = ["//visibility:public"],
+)
+
+alias(
+    name = "reflection",
+    actual = "//upb/reflection",
+    visibility = ["//visibility:public"],
+)
+
+alias(
+    name = "reflection_internal",
+    actual = "//upb/reflection:internal",
+    visibility = ["//visibility:public"],
+)
+
 alias(
     name = "text",
     actual = "//upb/text",
@@ -474,28 +363,6 @@ alias(
     visibility = ["//visibility:public"],
 )
 
-# Tests ########################################################################
-
-cc_test(
-    name = "def_builder_test",
-    srcs = [
-        "reflection/common.h",
-        "reflection/def_type.h",
-        "reflection/internal/def_builder.h",
-        "reflection/internal/def_builder_test.cc",
-    ],
-    deps = [
-        ":descriptor_upb_proto",
-        ":hash",
-        ":mem",
-        ":port",
-        ":reflection",
-        ":reflection_internal",
-        "@com_google_googletest//:gtest_main",
-        "@com_google_absl//absl/strings",
-    ],
-)
-
 # Internal C/C++ libraries #####################################################
 
 cc_binary(
diff --git a/upb/reflection/BUILD b/upb/reflection/BUILD
new file mode 100644
index 0000000000..380ae38e51
--- /dev/null
+++ b/upb/reflection/BUILD
@@ -0,0 +1,174 @@
+# Copyright (c) 2009-2021, Google LLC
+# All rights reserved.
+#
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+load("//bazel:build_defs.bzl", "UPB_DEFAULT_COPTS")
+load("//bazel:upb_minitable_proto_library.bzl", "upb_minitable_proto_library")
+load("//bazel:upb_proto_library.bzl", "upb_proto_reflection_library")
+load(
+    "//upb_generator:bootstrap_compiler.bzl",
+    "bootstrap_cc_library",
+    "bootstrap_upb_proto_library",
+)
+
+bootstrap_upb_proto_library(
+    name = "descriptor_upb_proto",
+    base_dir = "",
+    # TODO: Export 'net/proto2/proto/descriptor.upb.h' and remove "-layering_check".
+    features = ["-layering_check"],
+    google3_src_files = ["net/proto2/proto/descriptor.proto"],
+    google3_src_rules = ["//net/proto2/proto:descriptor_proto_source"],
+    oss_src_files = ["google/protobuf/descriptor.proto"],
+    oss_src_rules = ["//:descriptor_proto_srcs"],
+    oss_strip_prefix = "third_party/protobuf/github/bootstrap/src",
+    proto_lib_deps = ["//:descriptor_proto"],
+    visibility = ["//visibility:public"],
+)
+
+upb_proto_reflection_library(
+    name = "descriptor_upb_proto_reflection",
+    visibility = ["//visibility:public"],
+    deps = ["//:descriptor_proto"],
+)
+
+upb_minitable_proto_library(
+    name = "descriptor_upb_minitable_proto",
+    visibility = ["//visibility:public"],
+    deps = ["//:descriptor_proto"],
+)
+
+bootstrap_cc_library(
+    name = "reflection",
+    hdrs = [
+        "def.h",
+        "def.hpp",
+        "message.h",
+        "message.hpp",
+    ],
+    bootstrap_deps = [":internal"],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [
+        "//upb:base",
+        "//upb:mem",
+        "//upb:message",
+        "//upb:message_types",
+        "//upb:message_value",
+        "//upb:port",
+    ],
+)
+
+bootstrap_cc_library(
+    name = "internal",
+    srcs = [
+        "def_pool.c",
+        "def_type.c",
+        "desc_state.c",
+        "enum_def.c",
+        "enum_reserved_range.c",
+        "enum_value_def.c",
+        "extension_range.c",
+        "field_def.c",
+        "file_def.c",
+        "internal/def_builder.c",
+        "internal/def_builder.h",
+        "internal/strdup2.c",
+        "internal/strdup2.h",
+        "message.c",
+        "message_def.c",
+        "message_reserved_range.c",
+        "method_def.c",
+        "oneof_def.c",
+        "service_def.c",
+    ],
+    hdrs = [
+        "common.h",
+        "def.h",
+        "def.hpp",
+        "def_pool.h",
+        "def_type.h",
+        "enum_def.h",
+        "enum_reserved_range.h",
+        "enum_value_def.h",
+        "extension_range.h",
+        "field_def.h",
+        "file_def.h",
+        "internal/def_pool.h",
+        "internal/desc_state.h",
+        "internal/enum_def.h",
+        "internal/enum_reserved_range.h",
+        "internal/enum_value_def.h",
+        "internal/extension_range.h",
+        "internal/field_def.h",
+        "internal/file_def.h",
+        "internal/message_def.h",
+        "internal/message_reserved_range.h",
+        "internal/method_def.h",
+        "internal/oneof_def.h",
+        "internal/service_def.h",
+        "message.h",
+        "message.hpp",
+        "message_def.h",
+        "message_reserved_range.h",
+        "method_def.h",
+        "oneof_def.h",
+        "service_def.h",
+    ],
+    bootstrap_deps = [":descriptor_upb_proto"],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [
+        "//upb:base",
+        "//upb:hash",
+        "//upb:mem",
+        "//upb:message",
+        "//upb:message_accessors",
+        "//upb:message_types",
+        "//upb:message_value",
+        "//upb:mini_descriptor",
+        "//upb:mini_descriptor_internal",
+        "//upb:mini_table",
+        "//upb:port",
+    ],
+)
+
+cc_library(
+    name = "generated_reflection_support__only_for_generated_code_do_not_use__i_give_permission_to_break_me",
+    hdrs = [
+        "def.h",
+        "internal/def_pool.h",
+    ],
+    copts = UPB_DEFAULT_COPTS,
+    textual_hdrs = [
+        "//upb:port_inc",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//upb:mem",
+        "//upb:mini_descriptor",
+        "//upb:reflection_internal",
+    ],
+)
+
+cc_test(
+    name = "def_builder_test",
+    srcs = [
+        "common.h",
+        "def_type.h",
+        "internal/def_builder.h",
+        "internal/def_builder_test.cc",
+    ],
+    deps = [
+        ":descriptor_upb_proto",
+        "@com_google_googletest//:gtest_main",
+        "//upb:hash",
+        "//upb:mem",
+        "//upb:port",
+        "//upb:reflection",
+        "//upb:reflection_internal",
+        "@com_google_absl//absl/strings",
+    ],
+)
diff --git a/upb_generator/BUILD b/upb_generator/BUILD
index 79f2ac3649..723d490402 100644
--- a/upb_generator/BUILD
+++ b/upb_generator/BUILD
@@ -79,7 +79,7 @@ bootstrap_upb_proto_library(
     oss_strip_prefix = "third_party/protobuf/github/bootstrap/src",
     proto_lib_deps = ["//:compiler_plugin_proto"],
     visibility = ["//upb:friends"],
-    deps = ["//upb:descriptor_upb_proto"],
+    deps = ["//upb/reflection:descriptor_upb_proto"],
 )
 
 upb_proto_reflection_library(
@@ -97,7 +97,7 @@ bootstrap_cc_library(
         "common.h",
     ],
     bootstrap_deps = [
-        "//upb:reflection",
+        "//upb/reflection:reflection",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//protos_generator:__pkg__"],
@@ -119,8 +119,8 @@ bootstrap_cc_library(
     ],
     bootstrap_deps = [
         ":common",
-        "//upb:reflection",
-        "//upb:descriptor_upb_proto",
+        "//upb/reflection:reflection",
+        "//upb/reflection:descriptor_upb_proto",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//visibility:public"],
@@ -154,8 +154,8 @@ bootstrap_cc_library(
     ],
     bootstrap_deps = [
         ":plugin_upb_proto",
-        "//upb:descriptor_upb_proto",
-        "//upb:reflection",
+        "//upb/reflection:descriptor_upb_proto",
+        "//upb/reflection:reflection",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//protos_generator:__pkg__"],
@@ -177,7 +177,7 @@ bootstrap_cc_library(
         "names.h",
     ],
     bootstrap_deps = [
-        "//upb:reflection",
+        "//upb/reflection:reflection",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//protos_generator:__pkg__"],
@@ -244,8 +244,8 @@ bootstrap_cc_binary(
         ":names",
         ":plugin",
         ":plugin_upb_proto",
-        "//upb:descriptor_upb_proto",
-        "//upb:reflection",
+        "//upb/reflection:descriptor_upb_proto",
+        "//upb/reflection:reflection",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//visibility:public"],
@@ -283,8 +283,8 @@ bootstrap_cc_binary(
         ":names",
         ":plugin",
         ":plugin_upb_proto",
-        "//upb:descriptor_upb_proto",
-        "//upb:reflection",
+        "//upb/reflection:descriptor_upb_proto",
+        "//upb/reflection:reflection",
     ],
     copts = UPB_DEFAULT_CPPOPTS,
     visibility = ["//visibility:public"],