Under the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) is required to consider the impacts on air quality caused by previously unregulated sources, including nonroad engines and vehicles. In a previous report, EPA determined that engines used for marine applications, including both pleasure craft and commercial vessels, may contribute to emissions of regulated pollutants in some areas that fail to meet ambient air quality standards. Consequently, EPA has initiated efforts to further refine its understanding of the marine industry, including the products and markets of industry participants. The purpose of the report is to summarize data on the technical characteristics of marine engines and vessels and the financial characteristics of firms in the industry. The report contains no discussion of the environmental impacts associated with the marine industry or of the potential economic or financial effects that any future regulatory efforts may have.