Peer review has a long history at the U.S. Environmental Protection Agency and takes several different forms, some modeled after customary academic practice and some following statutory mandates. At the same time, EPA’s peer review practices have at times been uneven, varying in scope and quality. Beginning in 1992, responding to recommendations from the EPA Science Advisory Board (and, later, the General Accounting Office), EPA embarked on an agency-wide program to expand and strengthen its peer review policies and practices. The expansion process presented challenges on several different fronts and, after numerous stops and starts, led to a range of institutional changes. Today, agencies responding to the proposed OMB guidelines may face similar challenges. These agencies may benefit from learning about one agency’s approach to instituting more rigorous peer review practices.