In the last two years, we have heard a lot of news about drones, small autonomous flying vehicles. Flying robots have numerous advantages over ground vehicles: they can get access to environments where humans cannot get access to and, furthermore, they have much more agility than any other ground vehicle. Unfortunately, their dynamics makes them extremely difficult to control and this is particularly true in GPS-denied environments. In this talk, I will present challenges and results for both ground vehicles and flying robots, from localization in GPS-denied environments to motion estimation. I will show several experiments and real-world applications where these systems perform successfully and those where their applications is still limited by the current technology.