Within today's broad climate of evidence-based policymaking, impact evaluations increasingly influence policy and program decisions, including program funding, making these additional questions particularly salient. Recent methodological advances build on a long history of evaluation research, offering opportunities to unpack the so-called "black box" of programs and policies to understand "what, under what circumstances, and how?" On September 3rd and 4th, 2014, the Office of Planning, Research and Evaluation in the Administration for Children and Families, U.S. Department of Health and Human Services, convened a diverse group of participants from federal agencies, foundations, research firms, and academia to explore how existing and emerging methodological tools can advance research on social policies and programs. that researchers and program staff collaborate to systematically vary program components during the implementation of an intervention. Conference presenters discussed a variety of methods for designing variation in program components, including the multiphase optimization strategy (MOST); sequential, multiple assignment randomized trials (SMART); and rapid cycle evaluation. (author abstract)