The special section contained in this issue of Radio Science is the second of two which have been developed from papers presented at the 1987 symposium on the Effect of the Ionosphere on Communication, Navigation, and Surveillance Systems (IES 1987). This technical conference was jointly sponsored by the Naval Research Laboratory (NRL), the Office of Naval Research (ONR), the Air Force Geophysics Laboratory (AFGL), and the Army Communications-Electronics Command (USACECOM). The symposium was held in Springfield, Virginia on May 5–7, 1987 in cooperation with the Defense Nuclear Agency (DNA), the Naval Ocean Systems Center (NOSC), the Institute for Telecommunication Sciences (ITS), and the Voice of America (VOA). See the May-June 1988 issue of Radio Science for a more complete foreword (Radio Sci., 23, 209, 1988).