The 1973 Main Meeting sponsored by the U.S. National Committee of URSI and the 1973 IEEE International Antennas and Propagation Symposium will be held jointly at the Engineering Center of the Univers ity of Colorado. URSI and IEEE/G AP technical programs will be arranged separately except for the appropriate coordination. Authors are invited to present theoretical, experimental, and developmental papers in their fields of interest related to the following topics: radio measurements and standards, radio and nonionized media, ionospheric radio, magnetospheric radio, radio and radar astronomy, radio waves and transmission of informat ion, radio electronics, antennas, scattering and diffraction, electromagnetic theory, guided and unguided propagation of radio waves, and allied fields of radio physics, such as plasmas. Deadline for submission for all authors is May 28, 1973.