The paper provides an excellent overview of a research area of increasing interest. Motivations for research in the area of legged robots are clearly presented with a survey of early work in the area. Most of the paper is devoted to a description of the research performed by Marc Raibert at Carnegie-Mellon on hopping machines. Informative pictures are included to show the various generations of legged machines. In conclusion, the paper is informative and easy to follow, even for the reader new to this field. The references are more than adequate. Obviously, for the interested reader, the book published by the same author [1] is the best source of additional information.