The evaluation of environmental results from federal programs has increased significantly in recent years, both due to government-wide review requirements and agencies’ own interest in identifying potential program improvements. The USEPA’s Clean Water Act TMDL program has undertaken a self-evaluation of TMDL environmental results, program milestones, and explanatory factors that can collectively improve understanding of program results, provide a feedback loop for program managers, and lead to results-based program improvements. An effective approach to results analysis initially required the clarification of TMDL program goals and expectations, followed by identification of measurable results concepts that relate directly to progress toward program goals. We reviewed several recent analyses of the TMDL program and similar restoration programs to identify lines of evidence that showed possible results patterns that could be monitored with available databases. From the available evidence we developed evaluation metrics of three types. Response measures relate to environmental outcomes – interim improvements and full recovery in waters that have been addressed by the TMDL program. Programmatic measures track key milestones in the several-step TMDL program process from TMDL development and implementation through recovery. Explanatory measures assess linkages between environmental response results and potential causes; these measures are crucial for revealing why certain results are occurring and focusing attention on specific causes that should be addressed in program improvements. As this five-year effort accumulates new insights into TMDL results and their driving factors, the TMDL results analysis project will provide insights and evidence for improving the TMDL program. This paper provides the conceptual overview and unifying context for several papers comprising a special session on TMDL results analysis at the WEF TMDL 2007 conference.