Our first challenge problem is vision-based landing of an Unmanned Air Vehicle (UAV). Here, we use a camera on-board a UAV to perform motion estimation and to control its landing onto a possibly moving target. We present a robust multiple-view motion estimation algorithm and the implementation of a real-time vision system based on commercial off the shelf hardware. Through flight test results with our rotorcraft UAV testbed, we demonstrate a motion estimation accuracy of within 5cm in translation and 5° in orientation. Further, by placing the vision system in the control loop of our UAV, we demonstrate vision-based landing onto a stationary target and tracking of a moving target which simulates ship deck motion.