What's an ACO?

I've commented on numerous occasions here on the topic of Accountable Care Organizations (ACOs).  While the debate will continue regarding their viability and the likelihood of successful adoption across the industry, it's worthwhile understanding the basic concepts.  Health Affairs has developed a nice summary document on the topic.  Here's the intro:

The health care reform legislation enacted in March 2010 authorizes the Medicare program to contract with accountable care organizations (ACOs). These are networks of physicians and other providers that could work together to improve the quality of health care services and reduce costs for a defined patient population. This brief describes the ACO concept as set forth in the new legislation, discusses how ACOs might evolve over time, and reviews the challenges and opportunities facing health systems, physicians, administrators, insurers, patients, and policy makers as ACOs take shape.

More here.