diff --git a/libraries/AP_AHRS/AP_AHRS.h b/libraries/AP_AHRS/AP_AHRS.h
new file mode 100644
index 0000000000..1cd685d557
--- /dev/null
+++ b/libraries/AP_AHRS/AP_AHRS.h
@@ -0,0 +1,109 @@
+#ifndef AP_AHRS_H
+#define AP_AHRS_H
+/*
+  AHRS (Attitude Heading Reference System) interface for ArduPilot
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+*/
+
+#include <AP_Math.h>
+#include <inttypes.h>
+#include <AP_Compass.h>
+#include <AP_GPS.h>
+#include <AP_IMU.h>
+
+#if defined(ARDUINO) && ARDUINO >= 100
+	#include "Arduino.h"
+#else
+	#include "WProgram.h"
+#endif
+
+class AP_AHRS
+{
+public:
+	// Constructor
+	AP_AHRS(IMU *imu, GPS *&gps):
+		_imu(imu),
+		_gps(gps)
+	{
+		// base the ki values by the sensors maximum drift
+		// rate. The APM2 has gyros which are much less drift
+		// prone than the APM1, so we should have a lower ki,
+		// which will make us less prone to increasing omegaI
+		// incorrectly due to sensor noise
+		_gyro_drift_limit = imu->get_gyro_drift_rate();
+	}
+
+	// Accessors
+	void		set_centripetal(bool b) { _centripetal = b; }
+	bool		get_centripetal(void) { return _centripetal; }
+	void		set_compass(Compass *compass) { _compass = compass; }
+
+	// Methods
+	virtual void update(void) = 0;
+
+	// Euler angles (radians)
+	float		roll;
+	float		pitch;
+	float		yaw;
+
+	// integer Euler angles (Degrees * 100)
+	int32_t		roll_sensor;
+	int32_t		pitch_sensor;
+	int32_t		yaw_sensor;
+
+	// return a smoothed and corrected gyro vector
+	virtual Vector3f get_gyro(void) = 0;
+
+	// return the current estimate of the gyro drift
+	virtual Vector3f get_gyro_drift(void) = 0;
+
+	// reset the current attitude, used on new IMU calibration
+	virtual void reset(bool recover_eulers=false) = 0;
+
+	// how often our attitude representation has gone out of range
+	uint8_t renorm_range_count;
+
+	// how often our attitude representation has blown up completely
+	uint8_t renorm_blowup_count;
+
+	// return the average size of the roll/pitch error estimate
+	// since last call
+	virtual float get_error_rp(void) = 0;
+
+	// return the average size of the yaw error estimate
+	// since last call
+	virtual float get_error_yaw(void) = 0;
+
+	// return a DCM rotation matrix representing our current
+	// attitude
+	virtual Matrix3f get_dcm_matrix(void) = 0;
+
+protected:
+	// pointer to compass object, if enabled
+	Compass 	* _compass;
+
+	// time in microseconds of last compass update
+	uint32_t        _compass_last_update;
+
+	// note: we use ref-to-pointer here so that our caller can change the GPS without our noticing
+	//       IMU under us without our noticing.
+	GPS 		*&_gps;
+	IMU 		*_imu;
+
+	// true if we are doing centripetal acceleration correction
+	bool		_centripetal;
+
+	// the limit of the gyro drift claimed by the sensors, in
+	// radians/s/s
+	float           _gyro_drift_limit;
+};
+
+#include <AP_AHRS_DCM.h>
+#include <AP_AHRS_Quaternion.h>
+#include <AP_AHRS_HIL.h>
+
+#endif // AP_AHRS_H