Medicaid accountable care organizations (ACOs) have the potential to improve health care quality and control rising costs, particularly for complex, high-need beneficiaries. Given the prevalence of behavioral health conditions among this population and the related cost implications, coordinating behavioral health services within Medicaid ACOs may help states to dramatically improve quality of care and reap significant savings from avoidable emergency room and inpatient utilization. This brief, made possible by The Commonwealth Fund, outlines considerations to guide state Medicaid agencies in successfully integrating behavioral health services within ACOs.