Cities and regions present complex challenges in the areas of transport and environment. Consequently, local and regional authorities are keen to find efficient and integrated solutions for their environmental and traffic problems. The pressure on European cities and regions to implement the related EU regulations on air quality has led to a multitude of initiatives and isolated solutions, often with no common approach. Initiatives are required to develop better and more efficient solutions that go beyond the obligations of the related EU directives and that create synergies through the sharing of knowledge and experience. CITEAIR aims to develop improved and more efficient solutions to assess the impact of traffic on air quality in large urban areas. Through close cooperation, exchange of experience and joint developments with European Cities and Regions, the program will inform professional users and the public on the environmental situation and offer guidance on efficient measures to abate adverse environmental situations. Other municipalities are encouraged to contribute to the work via a user network.