Single crystals of ZnSe have been prepared by the vapor growth technique and optical and electrical measurements on these crystals are reported. Analysis of the reststrahlen reflection peak gives 0.026 ev for the transverse optical phonon energy. The longitudinal optical phonon energy is 0.031 ev as calculated from the transverse phonon energy, the static dielectric constant, &egr;0=8.1±0.3, and the high‐frequency dielectric constant, &egr;∞=5.75±0.1. The effective ionic charge calculated from the Szigetti formula is 0.7±0.1. Exciton absorption peaks associated with the valence and conduction bands in the vicinity of &Ggr; were observed at liquid hydrogen temperature with the principal peak at 2.81±0.01 ev. The exciton reduced mass 0.1m0combined with the room temperature electron‐to‐hole mobility ratio of 12, obtained by preliminary transport measurements onn‐ andp‐type ZnSe gives tentative values of 0.1m0and 0.6m0for the electron and hole masses, respectively.Reflectance was determined by various methods in the range 0.025 to 14.5 ev photon energy and was analyzed by the Kronig‐Kramers inversion method to obtain the optical constants in the 1 to 10 ev range. A number of peaks appear in the imaginary part of the dielectric constant.The first set of peaks, 2.7 and 3.15 ev, are believed to be due to exciton and interband transitions at &Ggr; with a spin‐orbit valence band splitting of 0.45 ev. The second set of peaks, 4.75 and 5.1 ev, are tentatively assigned to transitions atLwith a spin‐orbit splitting of 0.35 ev. Other peaks are observed at higher energies.