In the proposed monograph, we tried to summarize and systematize the experimental material accumulated over the past years (until 1960) on the diffusion of impurities and self-diffusion in various semiconductor materials. Some of this material was obtained in the diffusion processes laboratory of the Institute of Semiconductors of the USSR Academy of Sciences. The experimental material is preceded by chapters that outline the foundations of the theory of diffusion in solids and, in particular, in semiconductors.