This text aims to make mobile satellite communications understandable for communication engineers, candidates for an engineering degree, technicians, managers, and other decision makers such as financiers and regulators. It provides a systems oriented top-level view of mobile satellite communications. In particular, it focuses on Global Mobile Satellite Systems (GMSS) including active programmes such as Globalstar, IRIDIUM, ORBCOMM, ACeS, and Thuraya, or so-called the second generation mobile satellite systems class. The authors start with a brief description of three generations of satellite systems in use or planned in the telecommunications industry. Selected systems architectural trades are identified and explained to illustrate how various GMSS systems are formulated, developed and evaluated. It includes an examination of market demand trends, business trades, regulatory issues as well as technical considerations. Major issues are examined in trade study style to provide easy access to key information. Key systems drivers such as orbit trades between LEO’s, MEO’s, and GEO’s, frequency, protocols, customer bases, and regulatory and engineering issues are included. This book should appeal to individuals interested in the basic elements of Global Mobile Satellite Systems.