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 Communications. Photodetectors and Receivers. Atmospheric Channel. Optical Ground Station: Requirements and Design, Bidirectional Link Model and Performance. Reliability and Flight Qualification. Optical Satellite Networking. Coherent Laser Communications Links. All-Optical Satellite Communications Networks. Future Directions. Index