Fatigue is responsible for most of the mechanically-induced service failures of structural components encountered in industry. Therefore there is a pressing need for the development of nondestructive evaluation (NDE) methods to detect the development of fatigue damage, to monitor its progress and to predict impending failure of components as they come close to the end of their fatigue lives. Magnetic measurements offer promising techniques for these purposes, since the magnetic properties of ferromagnetic materials are sensitive to the microstructural changes caused by fatigue damage [1].