A predemonstration fusion device (PDFD) must provide the physics and technology information necessary to warrant design, construction, and operation of succeeding fusion reactors. This report sumarizes in three sections the bases for developing a PDFD. In the first section the philosophy and physics bases which will result in an economically viable fusion reactor are described. The characteristics and operating parameters of a PDFD which will provide a working demonstration of the concepts are given in the second section. In the final section the major research and development activities necessary to support construction and operation of the PDFD are outlined.