Abstract: An isothermal compressor apparatus and method, the apparatus including a compression chamber, a piston operable in the compression chamber and an evaporation chamber disposed in heat exchange relationship with the compression chamber, the evaporation chamber being interconnected with a closed refrigerant system. Valves control the flow of compressible gas through the compression chamber while heat exchange coils carry the compressed gas from the compression chamber through the evaporation chamber. The method includes compressing a gas and rapidly removing thermal energy imparted to the gas by the compression process with a refrigerant in the evaporation chamber.