Single phase chalcopyrite CuInSe2 coatings have been deposited by reactive cosputtering from Cu and In planar magnetron sources operated in an Ar+H2Se working gas. Effective sputtering yields from the conditioned Cu and In targets were approximately 0.7 and 0.5 atoms/unit charge, respectively. Sputtering rate, H2Se injection rate, and H2Se and H2 partial pressure measurements were consistent with the overall reaction Cu+In+2H2Se→CuInSe2+2H2. The formation of near-stoichiometric coatings appears to be aided at elevated temperatures by a reemission mechanism which removes excess In. Photovoltaic devices formed by evaporating CdS onto the sputtered CuInSe2 yielded short circuit currents of about 33 mA/cm2 and efficiencies of about 4%.