空气调节是包含温度、湿度、空气清净度以及空气循环的控制系统。冷气机／空调供应冷气、暖气或除湿的作用原理均类似，大部分利用冷媒在压缩机的作用下，发生蒸发或凝结，从而引发周遭空气的蒸发或凝结，以达到改变温、湿度的目的。冷气机及暖气机的效率会用性能系数来表示，是输入功和提供热能（或抽出热能）的比例值。

空气调节在台港澳通称「冷气」，因为该地区位处亚热带，气候潮湿炎热，空调的绝大部分作用只是制造冷气，鲜有需要制造暖气。

Air conditioning (often referred to as A/C or AC) is the process of altering the properties of air (primarily temperature and humidity) to more comfortable conditions, typically with the aim of distributing the conditioned air to an occupied space such as a building or a vehicle to improve thermal comfort and indoor air quality. In common use, an air conditioner is a device that lowers the air temperature. The cooling is typically achieved through a refrigeration cycle, but sometimes evaporation or free cooling is used. Air conditioning systems can also be made based on desiccants.