Research documenting the social and organizational benefits of collaborative planning has afforded collaborative planning an increasingly broader role in environmental policy and management. However, the bias toward evaluating the process and its social outcomes has resulted in a gap in knowledge of the impact collaborative environmental planning and management has on changing environmental conditions. This article attempts to reduce this gap by presenting a new performance evaluation framework that assesses collaborative environmental planning outputs and outcomes: both social and environmental. The case study of the Habitat Workgroup of the New York—New Jersey Harbor Estuary Program highlights the utility of this evaluation framework in assessing the quality of key outputs; the presence of outcomes (i.e., changes in social and environmental conditions); and observed relationships between process, outputs, and outcomes.