diff --git a/runtime/suspend_reason.h b/runtime/suspend_reason.h
new file mode 100644
index 0000000..27c4d32
--- /dev/null
+++ b/runtime/suspend_reason.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#ifndef ART_RUNTIME_SUSPEND_REASON_H_
+#define ART_RUNTIME_SUSPEND_REASON_H_
+
+#include <ostream>
+
+namespace art {
+
+// The various reasons that we might be suspending a thread.
+enum class SuspendReason {
+  // Suspending for internal reasons (e.g. GC, stack trace, etc.).
+  // TODO Split this into more descriptive sections.
+  kInternal,
+  // Suspending for debugger (code in Dbg::*, runtime/jdwp/, etc.).
+  kForDebugger,
+};
+
+std::ostream& operator<<(std::ostream& os, const SuspendReason& thread);
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_SUSPEND_REASON_H_