This account of the principles and applications of magnetooptics is aimed at the graduate physicist and electrical engineer, but assumes no specialist knowledge of magnetooptics. The text is divided into three main sections: the principles of magnetooptics, providing the historical background, with an emphasis on introducing practical considerations through examples taken from real-life situations; a survey of magnetooptic materials; and applications of magnetooptics in practical devices, including modulators, switches, memory devices and waveguides.