The Accountable Care Organization (ACO) model has received significant attention among policymakers and leaders in the healthcare community in the context of the ongoing debate over health reform, not only because of the unsustainable path on which the country now finds itself but also because it directly focuses on what must be a key goal of the healthcare system: higher value. The model offers a promising approach for achieving this goal. This article provides an overview of the ACO model and its role in the current policy context, highlights the key elements that will be common to all ACOs, and provides details of several challenges that may arise throughout the implementation process, including a host of technical, legal, and operational challenges. These challenges range from issues such as the organizational form and management of the ACO to analytic challenges such as the calculation of spending benchmarks and the selection of quality measures.