The important role that satellites play in the field of communications will be manifested by a large number of new satellite systems to be implemented within the next few years. These new systems will basically belong to two categories: (i) satellite networks for mobile/personal communications, mainly with handheld terminals, and (ii) satellite networks for broadband multimedia communications, mainly for fixed but also for portable and mobile terminals. This book gives an overview of both families of satellite systems. In Part I, the basics of geostationary and non-geostationary satellite constellations are dealt with, as well as the principles of satellite communications. Part II deals with satellite systems for mobile/personal communications and ad­ dresses various aspects of networking (multiple access, cell structure, routing, etc.); it also deals with technology, regulation, and financing. Part III is ded­ icated to future satellite systems for broadband communications (Internet, multimedia) and discusses satellite-specific aspects of broadband communi­ cations, in particular on the basis of ATM and TCP /IP. A survey of existing and planned satellite systems completes the book. The authors of this book are scientists at the German Aerospace Center, DLR (Deutsches Zentrum fiir Luft- und Raumfahrt) and work in the Digital Networks group of the Institute for Communications and Navigation.