The fragmented nature of the delivery and financing of health care in the United States, coupled with misdirected incentives dominating the payment structure, has driven national expenditures to be the highest in the world for health outcomes that are, at best, on par with the rest of the developed world. The Affordable Care Act of 2010 envisions a sustainable future by promoting health care delivery models that foster more efficient and effective health care services for both individuals and communities. As innovative models with the potential to contribute directly to lowering costs and improving outcomes, accountable care organizations (ACOs) present encouraging potential for leading the charge to redesign our health system. ACOs have become the programmatic and conceptual framework that is the centerpiece of moving our health care system from volume to value. Yet, with significant organizational, economic, legal, political, cultural, and conceptual challenges facing the formation and sustainable success of ACOs, the task remains formidable.