Freitas (Institute for Molecular Manufacturing) and Merkle (computer sciences, Georgia Institute of Technology) offer the first general review of the voluminous theoretical and experimental literature pertaining to physical self-replicating systems since the US National Aeronautics and Space Administration report and survey published in the middle 1980s. Their focus is on machine systems in which actual physical objects, not merely patterns of information, undertake their own replication in physical space—thus kinematic. The goal is to provide researchers a solid foundation from which to initiate their studies, and to help focus abstract philosophical discussions of self-replication in more concrete terms based on the emerging ability to make such machines.