Certain magnetic materials have optical properties that make them attractive for a wide variety of applications such as optical switches. This book describes the physics of one class of such magnetooptic materials, the insulating antiferromagnets. The authors summarize recent results concerning the structure, optical properties, spectroscopy, and magnetooptical properties of these materials. In particular, they consider magnetic phase transitions, symmetry effects, the linear magnetooptical effect, magnons, spectroscopic study of spin waves, photoinduced magnetic effects, and the effects of impurities.