diff --git a/BUILD b/BUILD
new file mode 100644
index 0000000..3c6b7b3
--- /dev/null
+++ b/BUILD
@@ -0,0 +1,21 @@
+# Copyright 2019 The Pigweed Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations under
+# the License.
+
+SUBDIRS = [
+    "pw_build",
+    "pw_preprocessor",
+    "pw_span",
+    "pw_status",
+    "pw_unit_test",
+]