The dramatic reduction of transmission loss in optical fibers coupled with equally important developments in the area of light sources and detectors has brought about a phenomenal growth of the fiber optic industry during the past two decades. The birth of optical fiber communication coincided with the fabrication of low-loss optical fibers and room-temperature operation of semiconductor lasers in 1970. Ever since, the scientific and technological progress in this field has been so phenomenal that we are already in the fifth generation of optical fiber communication systems within a brief span of 30 years. Recent developments in optical amplifiers and wavelength division multiplexing (WDM) are taking us to a communication system with almost “zero” loss and “infinite” bandwidth. Indeed, optical fiber communication systems are fulfilling the increased demand on communication links, especially with the proliferation of the Internet. This module, Optical Waveguides and Fibers, is an introduction to the basics of fiber optics, discussing especially the characteristics of optical fibers as regards their application to telecommunication (to be covered in Module 1.8, Fiber Optic Telecommunication) and fiber optic sensors.