ABSTRACT Used throughout history@ evaporative cooling is an effective means of air conditioning in hot and dry climates. Despite its effectiveness@ there is not substantial market penetration versus vapor compression systems in more humid climates. This is historically the case@ as in its most common form@ the direct evaporative cooler@ evaporative cooling suffers from substantial water consumption@ humidification of supply air@ and limited cooling to ambient wet bulb temperatures. The recent development of several innovative evaporative cooling cycles have broken through these traditional technical barriers. Dew point evaporative cooling@ using a novel heat exchanger and flow path arrangement@ can deliver unhumidified air below wet bulb temperatures consuming less water than direct evaporative and vapor compression coolers. Supply air temperatures approaching the dew point temperature are achieved in a single-stage unit with cooling capacity independent of the ambient air dry bulb temperature. Recently@ a prototype 5 ton rooftop unit delivered 80% energy savings relative to a conventional vapor compression system@ demonstrating the potential for dew point evaporative cooling in Zero Energy Design. This paper describes the technology fundamentals of dew point evaporative cooling through said heat exchanger and its context in the technology evolution of evaporative cooling@ ranging from direct to multi-stage indirect-direct evaporative cooling@ with performance comparisons under common operational conditions.