We develop wearable robotic devices to improve the efficiency, speed and balance of walking and running, especially for people with disabilities such as amputation or stroke. Our primary focus is to speed and systematize the design process itself by developing and using versatile hardware prosthesis and exoskeleton emulators and algorithms for human-in-the-loop optimization. We also perform basic scientific research on related topics, for example the role of ankle push-off in balance maintenance and the effects of arm swinging on energy economy in human gait. And we develop efficient autonomous devices, such as energy-efficient walking robots, ultra-low-power electroadhesive clutches, and unpowered exoskeletons that reduce the energy cost of walking.