The room temperature optical properties of single crystal MgF2were determined in the 4.1 eV–10.9 eV energy range, from transmission and near‐normal‐incidence reflectance measurements, and in the 11.0 eV–27.5 eV range, from reflectance measurements made at various angles of incidence. Sharp structure in the reflectance spectra of single crystal MgF2is associated with an exciton transition at 11.8 eV. Broader structure at higher energies is associated with an interband transition at 20.8 eV. The energy‐loss function for volume plasmons has a maximum at 24.5 eV which agrees well with the theoretical value. In addition, the optical properties of an evaporated film were determined in the range 11.0 eV to 29.5 eV, but structure in the reflectance spectrum is not as well defined. However, there is fair agreement with previously published optical constants of evaporated MgF2.