Thin films of Hf‐N, covering the entire composition range from pure Hf to overstoichiometric HfN, have been prepared by reactive magnetron sputtering. The structure of the films has been investigated by x‐ray diffraction, transmission electron microscopy, and scanning electron microscopy and the composition has been determined using Auger electron spectroscopy. A solubility of ≊30 at. % nitrogen is found in the &agr;‐Hf region. Above 30 at. % N a multiphase structure consisting of &agr;‐Hf, HfN, Hf3N2, and/or Hf4N3is found, which is not in agreement with the equilibrium structure. In the mononitride region a lattice parameter of ≊4.53 A˚ is observed. This value is slightly higher than reported bulk values due to intrinsic stress in the films. Increasing the nitrogen content above 50 at. % causes a distortion of the cubic symmetry of the lattice. This is first observed as an increase in the (111) interplanar spacing while other spacings decrease. Also a splitting of some reflections occurs at higher nitrogen contents. This phase transition is suggested to be due to a successive change from a cubic to a rhombohedral structure.