The Legged Learning Robot LittleDog is a quadruped robot 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 has four legs, each powered by three electric motors. The legs have a large range of motion and workspace. The motors are strong enough for dynamic locomotion, including climbing. 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 analysis. LittleDog development is funded by the DARPA Information Processing Technology Office.