This book contains fifteen chapters written by world leaders in various research areas in radio science. Each chapter describes the most exciting and important scientific developments that have taken place during the last three years. Fundamental information for a n--specialist is provided to facilitate understanding, and in addition, the most current developments are highlighted. Several chapters deal with issues of radio communication -- for example, satellite communication, mobile communication, and associated measurements -- and discuss the resultant problems in electro--magnetic spectrum congestion. Three chapters outline closely associated issues, namely new ways of modeling and designing systems, components and antennas. New developments and techniques are also covered in the scientific applications of radar, radio astromy, and plasma waves. In two chapters attention is devoted to quite different research issues at very low frequencies: those of atmospheric ise and interference, and the biological effects of power--line electromagnetic fields.