This paper discusses the operation of various types of evaporative or adiabatic saturation cooling systems. Particular attention is given to multistage systems and several unique and relatively unknown systems are discussed. It is shown that it is possible to have supply air temperatures equivalent to those of mechanical refrigeration systems in many parts of the country. Also shown is the effect of using evaporative assist cooling on hundred percent outside air systems and on conventional recirculating systems. A building was simulated in six U.S. cities selected for differing climates and demonstrated that evaporative cooling can save from ten to one hundred percent of the conventional mechanical cooling energy. System costs are still relatively high and payback relatively long in most cases.