Basic information on the unified system of tolerances and fits of parts of radio electronic equipment, microelectronics products, radio parts of printed and mounted installation is presented. Data on tolerances in the development of special-purpose microcircuits are given: hybrid integrated microcircuits of various degrees of integration, microassemblies, the selection of tolerances and fits to typical parts and connections is considered, depending on their design and technological features and operating conditions of radio-electronic equipment.