The Western States Air Resources Council (WESTAR), Western Regional Air Partnership (WRAP), and American Petroleum Institute (API) are co-sponsoring a scientific assessment on background ozone and future research needs, including a March 28-29 workshop in Denver. This assessment effort will focus on spatial and temporal variations of, and source contributions to, background ozone across the U.S. The assessment is focused on technical and scientific aspects of background ozone that are relevant to policy, but will not directly address policy. Additional information and agenda are posted on the WRAP website.