Automobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. Exhaust emissions control systems were first required on 1966 model year vehicles produced for sale in the state of California, followed by the United States as a whole in model year 1968. Their use became widespread in the following decades and now they are ubiquitous in industrialised nations and common in most others.
Emissions controls have been highly successful in reducing the emissions produced by motor vehicles in terms of quantity per distance traveled. However, substantial increases in the distance traveled by each vehicle, and equally substantial increases in the number of vehicles in use, have meant that the overall reduction in pollution has been much slower