This textbook was created on the basis of the training course, which for many years in various versions the authors read to the bachelors of the Institute of New Materials and Nanotechnologies of NUST MISIS. The first part of the textbook describes the laws of diffusion and the mechanisms of diffusion transfer of atoms in metals. The vacancy mechanism and its features are most fully disclosed. The second part deals with diffusion-based and diffusion-controlled processes, including phase growth, pore pore formation and annihilation, diffusion creep, sintering. Briefly touched on the basic provisions of linear thermodynamics of non-equilibrium processes and as an application of the process of thermal diffusion. To familiarize readers with the features of diffusion in non-crystalline solids: amorphous alloys and polymers In addition to the lecture material, the textbook contains problems with solutions and control questions to test the assimilation of the acquired knowledge. The textbook is intended for students, bachelors and masters specializing in the field of metal physics, metal science and physicochemical research in metallurgy . It may also be useful to graduate students, researchers, and engineers working in the steel, aviation, and engineering industries.