The United Kingdom uses an air pollution control system based on the best practicable means (b.p.m.) philosophy. The philosophy recognizes that a degree of air pollution is inevitable in present-day industrial society, and strives to optimize this pollution so that the total interest of society is best served. Account must be taken of health and amenity effects, of the capabilities of pollution arrestment techniques, of the finances of industry and effects on employment, and of the national need for the product. This paper describes the operation by H.M. Alkali and Clean Air Inspectorate of the four basic components of the b.p.m. philosophy: the setting of emission limits and other requirements which will give acceptable levels of ambient air pollution, prior approval of works' air pollution control equipment, continuing inspection and testing of the operation of control equipment, and prosecution of works managements where requirements are not met. It is shown that the b.p.m. philosophy compares favourably with alternative philosophies based on systems of statutory air quality standards or statutory emission standards. It is suggested that the b.p.m. philosophy can be developed and, with its involvement of workers, management, local interests and control authorities, is the system best able to meet the needs of air pollution control in the future.