Since the inception of the U.S. Environmental Protection Agency (EPA), considerable emphasis has been placed on the use of prospective policy analysis tools that aim to inform environmental decisions, including cost-benefit analysis and risk assessment. However, compared to the prevalence of ex ante analysis at the EPA to inform decisions, relatively little evaluation of these same environmental policies is conducted after implementation, to inform future policy development or to modify existing policies. This research considered processes and determinants that affect evaluation supply at the EPA. The research relied on archival documents, semi-structured interviews, and case studies of EPA’s ambient air, hazardous waste, and performance partnership programs. Ten key factors were identified across the three case studies that constituted both barriers to and facilitators of evaluation. This research concludes that evaluation has much to offer EPA decision-makers, and efforts to improve evaluation capacity will present organizational learning opportunities that can further support the agency's evidence-building practices, specifically improving the application and use of program evaluation at EPA.