This paper surveys available transparent infrared optical materials, their applications, selection criteria, and physical properties. Crystalline, polycrystalline, and amorphous (glassy) materials are considered. A few representative materials (KBr, KRS-5, MgF2, BaF2, A1203, Si02, ZnS, ZnSe, GaAs, Diamond, Ge, ZBLAN glass, As2S3 glass and Ge28SbI2Se60 glass) are discussed in detail and a complete and consistent set of property data are provided. Applications for these materials include bulk optics (lenses, prisms, beam splitters, etc.), windows, optical fibers, thin-film coatings (spectral and neutral density filters, protective and anti-reflective coatings), and opto-electronic devices.