We present a Visual Inertial Odometry system that enables the autonomous flight of Micro Aerial Vehicles in GPS denied and unstructured environments. The system relies on commercially available and affordable hardware both for sensing and computation. The algorithm runs in real time on an ARM based embedded micro-computer on-board an MAV. In experiments, we demonstrate the performance of the system both indoors and outdoors, in hand held an inflight scenarios. The achieved accuracy of the experiments is competitive with other research which uses custom designed hardware and desktop-grade processors.