All buildings are heated up during the day by the effects of solar radiation and cooled during the night by convection and radiant loss to the sky. This chapter deals with passive cooling techniques, which are the only way in a hot climate to achieve average temperatures inside a building lower than outdoors unless mechanical or active techniques are used. A passive cooling system is capable of transferring heat from a building to various natural heat sinks. A building designed using bioclimatic principle is a precondition for the application of passive cooling systems. Passive cooling systems can be classified according to the different heat sinks that are used: ambient air, upper atmosphere, water, and undersurface soil. The applicability of a given cooling system depends on the specified limits of the indoor climate, which varies with the type of building and outdoor climate.