Postwar developments in building have increased the importance of automatic controls for heating and air-conditioning installations because of the demand for comfortable environmental conditions and the large potential saving of fuel obtainable with appropriate controls. The reasons why the actual performance of heating controls is often unsatisfactory are considered.The characteristics of buildings and heating systems affecting the design and selection of automatic controls are discussed, and the principal elements of control systems are described, particular attention being devoted to improvements considered necessary to overcome difficulties in application.The application of these elements to typical systems of electrical heating, conventional central heating and air conditioning is then considered, and the paper concludes by discussing the problems of installation and maintenance and demonstrates how these can be alleviated by suitable design procedures.