AirCompare is an interactive Web site that provides the public with easy-to-access air quality information throughout the United States, based on specific health conditions of interest. This air quality information can help in making informed, health-protective decisions about moving, vacationing, or living in a given area. Results are based on the Air Quality Index which considers several principal air pollutants. The number of unhealthy days based on the levels of these pollutants is reported for locations of interest, providing a basis for comparing air quality.