AbstractThis paper reviews the history of the development of films for use in magneto-optic recording. A discussion of why these early attempts with films of MnBi and Europium compounds were abandoned is given. The current work on amorphous transition metal-rare earth alloys is then reviewed. The origins of the necessary perpendicular magnetic anisotropy are discussed. The ideal combination of properties desired are: a high room temperature coercivity, a large temperature coefficient of coercivity, a large perpendicular anisotropy constant, large Ms, thermal and environmental stability, and, depending on whether a reflection or absorption mode of operation will be used, a large Kerr rotation with large reflectivity or a large Faraday rotation with a small specific absorption. These factors, their control, bow they influence the recording performance and the limits on performance of these amorphous films are discussed.