This project contributes to the foundations of feedback control through the study of highly dynamic motions for 3D bipedal robots. Intellectual Merit: It is estimated that 70% of the earth's landmass is inaccessible to wheeled or tracked vehicles. This has stimulated interest in the design of robots that use legs as a means of locomotion. With legs, robots can step over obstacles or use sparse footholds (as in ladders). The research conducted under this NSF grant is enhancing the ability to design robots that can function in a wide range of natural environments. In particular, this work focuses on developing feedback control algorithms that will allow bipedal robots to walk, run, and turn rapidly, without stumbling and falling, thereby bringing closer the day when such robots can assist humans, and eventually stand in for them, in situations of extreme danger, such as when responding to a major industrial accident or a fire in a home. Broader Impacts: The research being conducted in this grant is enhancing the interest in STEM subjects, by giving tours of the 3D robotics laboratory to hundreds of students, from grade school through high school. More broadly, the work is being highlighted in the media, informing the public about the excitement of cutting-edge engineering research and how it benefits society. Dissemination: The research conducted in this grant is being published in leading peer-reviewed journals and conferences. The work is also available on public web sites and a YouTube channel, Dynamic Leg Locomotion. Videos from this channel have been featured worldwide on numerous television programs.