The manual describes in sufficient detail the approach to the study of relativistic nuclear interactions in the space of four-dimensional velocities, developed by academician A. M. Baldin. Other approaches are briefly considered. The most common modern detectors used in research in the field of relativistic nuclear physics are also described. It is told about the experiments carried out at the High Energy Laboratory (now the High Energy Physics Laboratory) of JINR in this area. Information is presented on the world physical accelerator centers working in the field of relativistic nuclear physics, and the most important physical results obtained in these centers.