Optic-flow is believed to be the main source of information allowing insects to control their flight. Some researchers have tried to apply this paradigm to small unmanned aerial vehicles (UAVs). So far, none of them has been able to demonstrate a fully autonomous flight of a free-flying system without relying on other cues such as GPS and/or some sort of orientation sensor (IMU, horizon detector, etc.). Getting back to the reactive approach suggested by Gibson (direct perception) and Braitenberg (direct connection from sensors to actuators), this chapter discusses how a few optic-flow signals can be directly mapped into control commands for steering an aircraft in cluttered environments. The implementation of the proposed control strategy on a 10- gram airplane flying autonomously in an office-sized room demonstrates how the proposed approach can result in ultra-light autopilots.