Optical waveguides are being investigated in terms of their use as ultra-wideband long-distance communication facilities and elements of miniature high-speed functional units. This book is the first monograph in which questions of the theory of almost all known types of optical waveguides are presented. It considers lens, continuous gas, fiber and flat (film) waveguides. Results are given for both regular and irregular (including statistically irregular) waveguides. The book also includes the most important questions of the theory of geometric and wave optics and the theory of light diffraction, necessary for understanding the operation of optical waveguides.