The development of legged robots with capabilities close to those of animals opens new and valuable possibilities, such as reaching distant points through rough or slopped terrains, detecting survivors in earthquake ruins or workers in mine tunnels, helping in fire-fighting or de-mining tasks, or even exploring planets. This research program aims at advancing the state of the art in legged locomotion and more specifically in efficient and agile quadruped locomotion through the development of novel designs and control methods. The goal of achieving efficiency, high-speed, robustness and versatility in quadruped robots is today feasible and will be pursued vigorously within the framework of this program.