The principles of magneto-optical (MO) recording and readout are reviewed and issues of thin film media design for MO disks are discussed. Essential criteria for improved media performance, and in particular, concepts of magneto-optical interactions in relation to multilayer designs for enhancing the polarization rotation in erasable magnetooptical media are considered. Examples of media design for improved performance are given. The role of sharp reflection edges such as those occurring near plasma edge resonances in metals is discussed. It is shown that rare earth hexaboride (RB6) reflector layers increase the polar Kerr rotation angle of MO media. Iso-Kerr rotation contours and iso-reflectance contours are developed to determine optimizing material properties for MO media design.