Optical response in magnetic media depends on their magnetic state, and this dependence manifests itself in magnetooptic (MO) effects [1]. Under normal circumstances, the action of magnetization even in media with nearly perfect magnetic ordering is weak, and special measures are required to make them observable. Usually a full advantage of the vectorial nature of the electromagnetic plane wave is taken by using the probing radiation with a defined (e.g., linear or circular) polarization state. In this introductory chapter, we give a brief overview of magnetooptics in magnetic materials. The main part that follows deals with the bases of magnetooptics from the phenomenological viewpoint of classical wave optics. The final part is devoted to the MO effects in multilayers. The information provided in this chapter allows the reader to immediately approach a broad class of MO problems encountered in practice.