Walking machines have advantages over traditional vehicles and have succeeded in carrying out many tasks that wheeled or tracked robots cannot do. However, their use in industry and services is limited in scope. This book presents some of the methods and techniques developed to deal with the problems that prevent legged robots being more widely used. Algorithms and methods are illustrated in a discussion of simulation and experiments tested on the SILO4 walking robot. Data from the experiments is available at http://www.iai.csic.es/users/silo4/. The historical development of quadrupeds, their advantages/disadvantages and potential uses, and the trade-off between quadrupeds and hexapods are discussed. Then the focus turns to the techniques applied to legged robots, including kinematic and dynamic models, soft computing techniques, virtual sensors, and software simulators. This book will be suitable for researchers, postgraduates and senior undergraduates in robotics, and, engineers working in industry.