Accountable Care Organizations (ACOs) were developed through the Affordable Care Act to encourage cost savings and high quality care through care coordination and management across provider networks. ACOs theoretically share governance, accountability for quality and costs, and risk and savings based on meeting quality metrics. In practice, ACOs originated from contracts with commercial insurers and focus accountability mostly on cost and process measures, though quality and patient satisfaction are increasingly emphasized. Performance is monitored against thresholds and targets, with informal influence, data credibility, and penalties or removal used to ensure accountability.