diff --git a/microdroid/payload/metadata.proto b/microdroid/payload/metadata.proto
new file mode 100644
index 0000000..0fa0650
--- /dev/null
+++ b/microdroid/payload/metadata.proto
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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
+ *
+ *      http://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.
+ */
+
+syntax = "proto3";
+
+package android.microdroid;
+
+// Metadata is the body of the "metadata" partition
+message Metadata {
+  uint32 version = 1;
+
+  repeated ApexPayload apexes = 2;
+
+  ApkPayload apk = 3;
+
+  string payload_config_path = 4;
+}
+
+message ApexPayload {
+  // Required.
+  // The apex name.
+  string name = 1;
+
+  string partition_name = 2;
+
+  // Optional.
+  // When specified, the public key used to sign the apex should match with it.
+  string publicKey = 3;
+
+  // Optional.
+  // When specified, the root digest of the apex should match with it.
+  string rootDigest = 4;
+}
+
+message ApkPayload {
+  // Required.
+  // The name of APK.
+  string name = 1;
+
+  string payload_partition_name = 2;
+
+  string idsig_partition_name = 3;
+}