The authors work at the Department of Automatic Control of the Industrial Automation Institute (IAI), which belongs to the Spanish Council for Scientific Research (CSIC). Over the past ten years, they have been involved in the research of walking robots techniques and have participated in the design and manufacturing of up to six different legged robots (climbing and walking) for diverse applications including ship building, terrain consolidation in civil-engineering works, educational robots and humanitarian demining. One of those robots (SILO4) is the basic model for simulation (geometric model) and experiments (real model) and there exist three replicas of this design which are owned by IAI-CSIC (Spain), University of Bourges (France) and University of Murcia (Spain). This robot is used for education and basic research purposes at these universities. The design drawings and some manufacturing hints are provided on the internet for those researchers willing to manufacture their own replicas. The basic material of this book is the result of four Ph.D. theses and three M.Sc. theses developed and/or advised by this book's authors, who have also some international experience: Dr. Gonzalez de Santos worked at the Robotics Institute (Carnegie-Mellon University) as a visiting scientist where he was involved in the development of the AMBLER walking robot; Dr. Garcia worked at the Leg Laboratory of the Massachusetts Institute of Technology as a visiting scholar where she was involved in the study of dynamic aspects of legged robots and Dr. Estremera is currently working at the University of Stanford (CA) with Professor Waldron, one of the most prominent researchers in legged locomotion.