In a cascade refrigeration system, two or more vapor-compression cycles with different refrigerants are used. The evaporation-condensation temperatures of each cycle are sequentially lower with some overlap to cover the total temperature drop desired, with refrigerants selected to work efficiently in the temperature range they cover. The low temperature system removes heat from the space to be cooled using an evaporator, and transfers it to a heat exchanger that is cooled by the evaporation of the refrigerant of the high temperature system. Alternatively, a liquid-to-liquid or similar heat exchanger may be used instead. The high-temperature system transfers heat to a conventional condenser that carries the entire heat output of the system and may be passive, fan, or water-cooled.