In recent years, several valuable books and review papers on various types of magnetic sensors, magnetometers, and their applications have appeared, but there is no up-to-date text fully covering this important, complex, and exciting field. The most comprehensive of the existing sources is, undoubtedly, Magnetic Sensors, edited by R. Boll and K, J. Overshott [1]. Although it was published over a decade ago, many parts of that book are still very valuable; it covers most of the sensor types (except for resonance sensors and SQUIDs), but not many of the problems of magnetometers and their applications. Solid State Magnetic Sensors, written by Roumenin [2], covers only semiconductor sensors and SQUIDs. That book is oriented toward interesting but often rather impractical devices, such as magnetotransistors and carrier-domain magnetometers. Hall Effect Devices, written by R.S.Popovic, is still valuable but very specialized.