This book (which has 15 chapters) covers the principles, challenges, methodologies, techniques, and applications of Free Space Optical Communication for an audience of engineers, researchers, scientists, designers, and advanced students. Free Space Optical (FSO) Communication uses light propagation in free space (air, outer space, and vacuum) to wirelessly transmit data for telecommunications and communication networking. FSO Communication is a key wireless and high-bandwidth technology for high speed large-capacity terrestrial and aerospace communications, which is often chosen as a complement or alternative to radio frequency communication. The propagating optical wave can be influenced negatively by random atmospheric changes such as wind speed, temperature, relative humidity, and pressure, thermal expansion, earthquakes, and high-rise buildings.