Communications satellites have become a proven means of providing reliable, economical, and flexible communications, not only between large communications centers, but to remote areas of the world as well. The initial system, INTELSAT, which first connected large communications centers in the U.S., Canada, and Europe, has expanded to include most of the small countries around the world. Leased satellite capacity permits many countries to interconnect their cities and villages. In addition, a special purpose system (MARISAT) is available to provide reliable, continuous, and economical service to ships at sea. The economic viability of these systems is no longer questioned. Instead, new questions relating to system optimization, such as earth station antenna size and allocation of resources to R & D efforts, are of increasing interest. In the past, the earth station size was generally determined by the very limited satellite capacity, and R & D expenditures were allocated for the accomplishment of fairly close range objectives. Now that the technology is maturing and the systems are operational, the questions of optimization can be addressed more realistically.