The automotive gasoline engine has been under heavy attack as a source of air pollution, and is now the subject of a very large program of research and development to reduce its undesirable vehicle emissions. The quantity of emissions that can reasonably be tolerated in different areas of the U.S. is presently unknown because of lack of information concerning air movements and air quality standards for man and plants. It is important that this information be made available as quickly as possible because the cost of emission controls of all types will rise rapidly. With rapidly rising costs for air pollution control from all sources, cost-value analyses are urgently needed for economy.Major reductions of the undesirable exhaust emissions of present powerplant systems have been made during the last few years and will continue to be accomplished, under the impetus of air pollution requirements and regulations. Improved versions of automotive piston engines will continue for many years to be the main source of power for highway transportation.There is a place for battery-powered vehicles in small size and short-range applications, especially for areas with serious air pollution. They will, however, require batteries with much greater energy and power density, and greatly reduced cost, before they will achieve significant use. The increased use of central station atomic energy in the future will give added advantages to battery-electric vehicles.Any successful program for reduction of exhaust emissions from vehicles must include an effective engine inspection and maintenance program. From the standpoint of trained personnel and necessary facilities and instrumentation, this constitutes a major problem. Industry, government, the technical societies, and individuals all have key roles to play in the rapidly growing effort to reduce vehicular emissions.