Legged robots have distinct advantages over their wheeled counterparts when working in arbitrarily complex terrains - they can generally cross obstacles more easily, and exhibit greater adaptability. These features are important in several applications such as exploration, maintenance, intervention and service. These application domains are beyond the realm of traditional manufacturing robots. Bipeds are especially interesting because humans are two-legged, and places meant to be occupied by humans, such as homes and offices, may soon be co-inhabited by both humans and humanoids in the not distant future.