This book treats the phenomena associated with the propagation of short radio waves between terminal points, whether they be the radar antenna serving a dual purpose or the antennas of a communications system. The intention is to present a summary of the state of knowledge in the microwave propagation field at the close of the war. There has been no attempt to produce either a handbook or textbook, but only an interim report on a rapidly changing subject. An attempt has been made to survey all relevant information that was available, from whatever source, and to summarise as much of it as was feasible.