Epitaxial garnet films have been prepared by rf sputtering from a polycrystalline gadolinium iron garnet target onto single-crystal substrates of YAG. Epitaxy is achieved on all orientations of the substrate, either in situ when depositing at ≥500°C, or during post-deposition crystallization of amorphous or partially crystallized films deposited at <500°C. The compensation temperature in epitaxial films depends strongly on the deposition temperature. The lowest compensation temperatures are found in films prepared at the highest deposition temperatures. Flims prepared on glass substrates at elevated deposition temperatures are iron deficient and crystallize in at least two phases, Gd3Fe5O12 and GdFeO3. The iron deficiency in these films is assumed to be caused by a variation with temperature in the net cation sticking coefficients. No GdFeO3 phase is found in epitaxial films prepared at the same elevated deposition temperatures, although these films should also be iron deficient. It is believed that they are, in fact, iron deficient, but that they crystallize with the garnet structure with iron vacancies in one of the iron sublattices, giving rise to some of the unexpected magnetic and structural properties of the films. © 1969 The American Institute of Physics.