LittleDog is a quadruped robot designed for research on learning locomotion. Scientists at leading institutions use LittleDog to probe the fundamental relationships among motor learning, dynamic control, perception of the environment, and rough-terrain locomotion. LittleDog is used at MIT, Stanford, Carnegie Mellon, Univ. Pennsylvania and IHMC as part of a DARPA-funded program on advanced robotics. LittleDog has four legs, each powered by three electric motors. The legs have a large range of motion. The robot is strong enough for climbing and dynamic locomotion gaits. The onboard PC-level computer does sensing, actuator control and communications. LittleDog's sensors measure joint angles, motor currents, body orientation and foot/ground contact. Control programs access the robot through the Boston Dynamics Robot API. Onboard lithium polymer batteries allow for 30 minutes of continuous operation without recharging. Wireless communications and data logging support remote operation and data analysis. LittleDog development is funded by the DARPA Information Processing Technology Office.