<P>Introduction. Systems Engineering and Design Drivers. Pointing, Acquisition, and Tracking. Laser Transmitters: Coherent and Direct Detections. Flight Optomechanical Assembly. Coding and Modulation for Free-Space Optical<BR>Communications. Photodetectors and Receivers. Atmospheric Channel. Optical Ground Station: Requirements and Design, Bidirectional Link Model and Performance. Reliability and Flight Qualification. Optical Satellite Networking: The Concept of a Global Satellite Optical Transport Network. Future Directions. Index.</P>