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ABSTRACT (Maximum 200 words)A symposium entitled "Radio Propagation in the Ionosphere and Magnetosphere: Theory and Application" was convened at the 23rd General Assembly of URSI, August 28 through September 5, 1990. Of-the 49 papers presented at this symposium, 13 were selected for publication in Radio Science, Volume 27, Number 2, March-April 1992.These papers cover a broad field of ionospheric and magnetospheric propagation of both experimental and theoretical nature. At the 23rd General Assembly (GA) of the International Union of Radio Science (URSI) held in Prague, Czechoslovakia, August 28 through September 5, 1990, a Joint Symposium 2 (JS2), cosponsored by Commissions G and H of URSI, was convened. This symposium was entitled "Radio Propagation in the Ionosphere and Magnetosphere: Theory and Application." The undersigned were appointed as conveners by Commission G Chair, Henry Rishbeth, and Commissio. H Chair, Hiroshi Matsumoto. For this symposium, altogether 49 papers were received and presented by authors from 12 countries around the world. The richness and diversity of the work marked a milestone of our progress in this field. Many scientific leaders in the radio science community felt that it was perhaps a good opportunity to collect these papers and have them published in one journal as a special section. After a survey of all authors, strong interest had been expressed in publishing them in Radio Science. With the strong support of the authors and the Editors of Radio Science we proceeded to contact the authors and to process the papers after having received them.The papers presented at the JS2 of URSI GA covered a vast field. In terms of geographic regions, propagation paths under study took place in high latitudes where the auroral ionosphere, under the perpetual influence of penetrating convective electric fields of magnetospheric origin, was often very disturbed, or in equatorial latitudes where the ionosphere was subject to equatorial dynamics and plasma instabilities, or over long paths traversing many different regions of the globe. In terms of wave frequencies the waves could be in the VLF band propagating in the Earthionosphere waveguide mode; they could also be ion cyclotron waves and whistler waves which were slowly propagating and highly dispersive; they could also be in the HF to SHF bands where effects produced by the inhomogeneous and anisotropic natur...