Doctors on deck. ACOs led by doctors seek to manage costs, quality and hospital relationships.

Most of the first crop of ACOs in the Medicare Shared Savings Program are owned and operated by physicians without formal participation of a hospital in the efforts to improve quality and curb costs. "There were some people who feared that the only entities that would participate would be hospital-dominated systems," says Jonathan Blum, director of the Center for Medicare Management at the CMS, left. "That has not happened".