diff --git a/common/env.go b/common/env.go
new file mode 100644
index 0000000..e33a025
--- /dev/null
+++ b/common/env.go
@@ -0,0 +1,47 @@
+// Copyright 2015 Google Inc. All rights reserved.
+//
+// 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.
+
+package common
+
+import (
+	"android/soong/env"
+
+	"github.com/google/blueprint"
+)
+
+// This file supports dependencies on environment variables.  During build manifest generation,
+// any dependency on an environment variable is added to a list.  During the singleton phase
+// a JSON file is written containing the current value of all used environment variables.
+// The next time the top-level build script is run, it uses the soong_env executable to
+// compare the contents of the environment variables, rewriting the file if necessary to cause
+// a manifest regeneration.
+
+func EnvSingleton() blueprint.Singleton {
+	return &envSingleton{}
+}
+
+type envSingleton struct{}
+
+func (c *envSingleton) GenerateBuildActions(ctx blueprint.SingletonContext) {
+	envDeps := ctx.Config().(Config).EnvDeps()
+
+	envFile := ".soong.environment"
+
+	err := env.WriteEnvFile(envFile, envDeps)
+	if err != nil {
+		ctx.Errorf(err.Error())
+	}
+
+	ctx.AddNinjaFileDeps(envFile)
+}