Improvement and progress in the field of creating structures with a responsible purpose in various branches of industry prompts the scientific community to improve and develop new materials with increased operational characteristics, which combine high strength, hardness with high plasticity at room and elevated temperatures, corrosion resistance and other important physical and mechanical properties. Permanent search and fundamental research in this area led to the emergence of a new unique class of materials—high-entropy alloys—complex multicomponent systems, which have a high entropy factor and are characterized mostly by the structure of solid solutions. In recent years, great attention is paid not only to the development of structural high-entropy materials, but also to the creation of high-entropy solders, which are used to obtain non-separable joints by brazing. This review presents the structure of high-entropy solders based on transition $d$-elements with a single-phase structure of a solid solution, eutectic, which are compatible with the base metal and provide the necessary temperature range of brazing, a good level of its wetting and mechanical characteristics of the soldered joints. The peculiarities of formation of the structure of soldered joints, when using a high-entropy solder, in the presence of a concentration gradient and mutual diffusion processes at the interphase boundary and with obtaining high-entropy crystal structures in the soldered seams are considered.