This is the first book in the series that is being called The Reviews of Infrared and Millimeter Waves. The series will contain the manuscripts of invited papers from conferences on this subject. This first book contains some of the invited papers from the XXth General Assembly of the Union-Radio-Scientifique Internationale, Washington, August, 1981. We were asked by the URSI Cornmittee to organize a two day symposium on millimeter and submillimeter waves This required the difficult choice of five topics which turned out to be (1) Ultra-low Noise Millimeter Wave Rec~ivers (Detectors and Mixers), (2) Free Electron Maser and Gyrotron, (3) Measurements of Power and Noise Power, (4) Complex Dielectric Properties of Solids and Liquids, and (5) Radioastronomy. We have not yet collected all the m . . nuscripts and perhaps we never shall because the tine-. consur. J. ing effort required to prepare a comprehensive review nanuscript works a hardship on research scientists who are already overburdened. 've are particularly grateful, therefore, to the authors lVho have worked so hard to contribute the chapters to this book. The first four chapters contibute to the timely topic of detectors, nixers and re- ceivers. These authors: Tucker, Feldman, Rudner, Okamura, Hogg and their well-known colleagues have been among the leaders in this exciting emerging field for the past few years. The fifth chapter by Sakai and Genzel is the most comprehensive treatment of the metal mesh filter science that can be found in one place.