In the 1970s, it was managed care organizations. In the 1990s, it was vertically integrated health care systems. In the 2010s, the fashionable concept for improving health care, apparently beloved by left-wing policy wonks and right-wing health care executives is the "accountable care organization." (ACO). Development of the ACO is funded by the recently passed US health care reform legislation. The official definition of ACO from the US Center for Medicare and