A review is given of some of the fundamentals of fiber optical transmission systems including fiber optical waveguides, optical sources, and photodetectors. Fiber optical systems can, in principle, compete with twisted pair, coaxial cable and waveguide facilities in virtually all sectors of the communication network. These systems are attractive because fiber optical waveguides are potentially inexpensive, have miniature cross section, are strong and flexible, have light weight, and can transmit broad band signals over long distances with low distortion. Recent advances in glass materials technology and fiber fabrication procedures have resulted in fiber waveguides with losses as low as 4dB/km in the important wavelength region around 8200A corresponding_ to the output of the GaA1As laser. The range of applications of fiber optical systems extend from short and long haul communications to wiring within buildings and between computer terminals, as well as to a variety of military applications which capitalize on the unique properties of glass fibers.