diff --git a/libraries/AP_Vehicle/AP_Vehicle.h b/libraries/AP_Vehicle/AP_Vehicle.h
index 308cde357f..6097ec5d17 100644
--- a/libraries/AP_Vehicle/AP_Vehicle.h
+++ b/libraries/AP_Vehicle/AP_Vehicle.h
@@ -19,6 +19,8 @@
   parameters needed by multiple libraries
  */
 
+#include "ModeReason.h" // reasons can't be defined in this header due to circular loops
+
 #include <AP_Baro/AP_Baro.h>
 #include <AP_BoardConfig/AP_BoardConfig.h>     // board configuration library
 #include <AP_BoardConfig/AP_BoardConfig_CAN.h>
@@ -49,6 +51,8 @@ public:
 
     static AP_Vehicle *get_singleton();
 
+    bool virtual set_mode(const uint8_t new_mode, const ModeReason reason) = 0;
+
     /*
       common parameters for fixed wing aircraft
      */
diff --git a/libraries/AP_Vehicle/ModeReason.h b/libraries/AP_Vehicle/ModeReason.h
new file mode 100644
index 0000000000..2ef46b684a
--- /dev/null
+++ b/libraries/AP_Vehicle/ModeReason.h
@@ -0,0 +1,54 @@
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+// interface to set the vehicles mode
+enum class ModeReason : uint8_t {
+  UNKNOWN,
+  RC_COMMAND,
+  GCS_COMMAND,
+  RADIO_FAILSAFE,
+  BATTERY_FAILSAFE,
+  GCS_FAILSAFE,
+  EKF_FAILSAFE,
+  GPS_GLITCH,
+  MISSION_END,
+  THROTTLE_LAND_ESCAPE,
+  FENCE_BREACHED,
+  TERRAIN_FAILSAFE,
+  BRAKE_TIMEOUT,
+  FLIP_COMPLETE,
+  AVOIDANCE,
+  AVOIDANCE_RECOVERY,
+  THROW_COMPLETE,
+  TERMINATE,
+  TOY_MODE,
+  CRASH_FAILSAFE,
+  SOARING_FBW_B_WITH_MOTOR_RUNNING,
+  SOARING_THERMAL_DETECTED,
+  SOARING_THERMAL_ESTIMATE_DETERIORATED,
+  VTOL_FAILED_TRANSITION,
+  VTOL_FAILED_TAKEOFF,
+  FAILSAFE, // general failsafes, prefer specific failsafes over this as much as possible
+  INITIALISED,
+  SURFACE_COMPLETE,
+  BAD_DEPTH,
+  LEAK_FAILSAFE,
+  SERVOTEST,
+  STARTUP,
+  SCRIPTING,
+  UNAVAILABLE,
+};