A structure created to air-cool hot water which has been condensed from steam used in a steam turbine generator. The water used in energy generation must be returned to a temperature relatively close to its original temperature before it can be returned to the surrounding habitat. If it is insufficiently cooled, the excess heat can cause serious problems for that habitat by altering biological balance.

Tower designs fall into two distinct categories: forced draft and natural draft. Forced draft systems use blowers or some form of artificial convection to force large amounts of air past shallow tanks or tubes of water. Natural draft systems use the natural airflow of the environment, known as chimney effect, to convect air past the hot water.

Cooling towers are often the largest visible structures of combustion turbine and nuclear generating facilities. The distinctive appearances of nuclear plants is usually defined by the shape of the cooling towers used by the plant; the actual reactors typically require only a fraction of the space needed by these towers.

The increasing popularity of cogeneration systems may result in substantially fewer and smaller cooling towers being constructed in the future.

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