Diffusion profiles and the solubility of Cu in Ge were measured in the temperature interval 850–1200 K by means of the spreading‐resistance technique. From these data it is concluded that the diffusion of Cu in Ge involves the interchange between a highly mobile interstitial configuration, Cui, and a practically immobile substitutional configuration, Cus, with the aid of vacancies,V, via the so‐called dissociative mechanism, Cui+V&rlarr2;Cus. The excellent agreement of the values of the vacancy contribution to the tracer self‐diffusion coefficient in Ge, as calculated from our diffusivity and solubility data on Cu in Ge, with directly measured values of the71Ge tracer self‐diffusion coefficient from the literature demonstrates that self‐diffusion in Ge occurs via vacancies. A comparison with the mechanisms of Au and self‐diffusion in Si is presented.