The Affordable Care Act established the Center for Medicare and Medicaid Innovation to test innovative payment and service delivery models. The goal is to reduce program expenditures while preserving or improving the quality of care provided to beneficiaries of Medicare, Medicaid, and the Children's Health Insurance Program. Central to the success of the Innovation Center is a new, rapid-cycle approach to evaluation. This article describes that approach--setting forth how the Rapid Cycle Evaluation Group aims to deliver frequent feedback to providers in support of continuous quality improvement, while rigorously evaluating the outcomes of each model tested. This article also describes the relationship between the group's work and that of the Office of the Actuary at the Centers for Medicare and Medicaid Services, which plays a central role in the assessment of new models.