The U.S. Environmental Protection Agency's New Source Review (NSR) programs are designed to help ensure that the construction or modification of factories, electric-generating facilities and other large stationary sources of pollutants will meet emissions criteria. EPA revised the programs in order to provide flexibility and allow for improved energy efficiency in American industry without damaging the environment. However, critics argue the revisions could slow progress in cleaning the nation's air, potentially damaging human health. This interim report provides a synthesis of relevant background information and describes the approach the committee will use to assess the potential impact of the NSR revisions. Conclusions will be issued in a final report later this year.