In spite of the efforts of related industries, the air pollution situation particularly in urban areas of Japan is not satisfactory. It has been shown that air pollution is caused mainly by increased automotive traffic and increased penetration of diesel vehicles. Air-quality problems will become much more complicated and more severe in the future with increased emphasis on reducing air pollution and global warming. These situation will require continuous reduction of automobile emissions.In order to obtain cleaner exhaust emissions, cooperative studies between vehicle and fuel technologies are considered to be essential, and AQIRP in the United States and Auto/oil Program in Europe were already conducted to develop the best combination of measures for air pollution improvement.In 1996, Japan Clean Air Program (JCAP) was launched by Petroleum Energy Center (PEC) in cooperation with the Petroleum Association of Japan (PAJ) and the Japan Automobile Manufacturers Association (JAMA). This program was planned, referring to U.S. AQIRP and European Auto/Oil Program, in order to improve air quality in Japan, taking into consideration Japan's unique conditions such as its regulations, driving patterns, fuel quality, air quality level, climate, and so on. Participants in the program consist of not only from industries but also those from government and academia, so that the study will be reflected in the future environmental policies. As a new attempt, JCAP is introducing fundamental combustion analysis to elucidate the results of fuel/engine matrix tests and health-effects studies in order to understand air quality requirements. Based on results of the emission test of future vehicle/engine and fuel technologies, JCAP will predict air-quality in 2010, and will evaluate the costs and effects. This program is planned to be completed in 2002 spring.This paper describes JCAP's objectives and design, including current air-quality situation in Japan, regulations regarding automotive emissions and fuel-quality, technological development, and the features of JCAP.