Accountable care organization (ACO) is an umbrella term for a major switch in contracting between providers and public or private payers. In an ACO model, a group of providers, operating as a legal entity, contracts to assume some portion of the risk for cost and quality for a panel of beneficiaries through a variety of value-based payment models over a specified period of time. ACOs include primary care services. The U.S. CMS Distributed Shared Savings Program, which began operation in 2012, is one version of this model.