In the three decades since the U.S. Environmental Protection Agency (EPA) was created, the agency's scientific and technical practices and credibility have been independently assessed many times in reports from the National Research Council (NRC), EPA Science Advisory Board, General Accounting Office, and many other organizations; in congressional oversight and judicial proceedings; and in countless criticisms and lawsuits from stakeholders with interests in particular EPA regulatory decisions. As a previous independent panel put it in the 1992 report Safeguarding the Future: Credible Science, Credible Decisions, EPA's policy and regulatory work receives a great deal of public attention, but the agency's scientific performance typically receives a similar degree of attention only when the scientific basis for a decision is questioned. Thus, strong scientific performance is important not only to enable EPA to make informed and effective decisions, but also to gain credibility and public support for the environmental protection efforts of EPA and the nation. This report is the fourth and final one in a series prepared by two independent expert committees convened by the NRC in response to a request from Congress and to subsequent, related requests from EPA. The Committee on Research Opportunities and Priorities for EPA-the companion committee in this study-was charged to provide an overview of significant emerging environmental issues, identify and prioritize research themes most relevant to understanding and resolving those issues, and consider the role of EPA's research program in the context of research being conducted or supported by other organizations. That committee published an interim report in 1996 and a final report, Building a Foundation for Sound Environmental Decisions, in 1997. The Committee on Research and Peer Review in EPA was charged to evaluate research management and scientific peer-review practices in the agency. The committee published