Accountable Care Organizations (ACOs) are entities that agree to provide coordinated care to enrollees and are eligible for incentive payments if they improve health and reduce costs. ACOs have been used in Medicare for several years but, until recently, much less so in Medicaid. That is beginning to change. This Fact Sheet describes Medicaid ACOs and provides a brief history of the evolution of ACOs. It also highlights how some states are using ACOs and the similarities and differences between ACOs in different states, particularly those affecting people with disabilities. Finally, it provides tips for advocates when their states consider or operate Medicaid ACOs.