The book is written by professors and doctoral researchers from the Norwegian University of Science and Technology. The authors are also associated with SINTEF, which is a Norwegian research organization that conducts applied research for the industry. NTNU and SINTEF have had cooperating research activities related to modelling, physical implementation, and control of snake robots since 2001. Over these years, our research group has acquired a leading role within this field with numerous publications in peer-reviewed conferences and top-ranked international journals. The research activity has resulted in the development of several snake robots which have attracted much national and international attention, and has also helped establish and strengthen relations with key research communities working with snake robots in Japan, USA, and the Netherlands. Nonlinear control of mechanical systems, which includes snake robot research, has been the main research activity by the research group of the authors for several decades with excellent results.