Rare earth materials best suited for the growth of the optical and glass industries are identified, with emphasis on their suitability for commercial, industrial, scientific, and medical products. The optical properties of the heavier rare earth metals are reviewed, including the most practical and accurate methods for the measurement of optical properties and a discussion of some errors arising from the samples. A survey of optical data is presented, including the data from electronenergy loss measurements, magneto-optic effects, and modulation spectroscopy. The optical properties of rare earth metals are strictly those of the transition metals; the 4f electrons and magnetic order play minor but observable roles. The optical properties of rare earth metals yield vital information on the electronic structure of the rare earths that are several electron volts or more away from the Fermi level; therefore, they complement the Fermi surface measurements by providing a test for calculated or intuitive band structures.