Accountable care organizations (ACOs) are forming in communities across the country. In ACOs, health care providers take responsibility for a defined patient population, coordinate their care across settings, and are held jointly accountable for the quality and cost of care. This issue brief reports on results from a survey that assesses hospitals' readiness to participate in ACOs. Results show we are at the beginning of the ACO adoption curve. As of September 2011, only 13 percent of hospital respondents reported participating in an ACO or planning to participate within a year, while 75 percent reported not considering participation at all. Survey results indicate that physician-led ACOs are the second most common governance model, far exceeding payer-led models, highlighting an encouraging paradigm shift away from acute care and toward primary care. Findings also point to significant gaps, including the infrastructure needed to take on financial risks and to manage population health.