Recent advances in semiconductor technology have made possible the fabrication of structures whose dimensions are much smaller than the mean free path of an electron. This book gives the first thorough account of the theory of electronic transport in such mesoscopic systems. Beginning with coverage of fundamental concepts, the book presents a detailed account of transmission function formalism which is used to describe three key topics in mesoscopic physics: the quantum Hall effect, localization, and double-barrier tunneling. Other sections include a discussion of optical analogies to mesoscopic phenomena, followed by a concluding description of the non-equilibrium Green's function formalism and its relation to the transmission formalism. Complete with problems and solutions, the book will be of great interest to graduate students of mesoscopic physics and nanoelectronic device engineering, as well as to established researchers in these fields.