The most celebrated “bend the curve” idea from the Patient Protection and Affordable Care Act (PPACA) is the Medicare accountable care organization (ACO). ACOs are intended to be integrated health plans, with hospitals, physicians, and other health services providers working together in a coordinated patient delivery system. The Obama administration and the law’s strongest proponents repeatedly cited ACOs both during consideration of the law and in the years since its passage as evidence that Obamacare was more than just a coverage expansion measure. The public was told that ACOs, along with a few other “delivery system reforms,” would transform the way hospitals and physicians interact with patients and thus slow the rate of growth of the nation’s health spending while improving quality. In sum, ACOs were promoted as a key to a better and more affordable health system. "It is clear that the ACOs of the PPACA variety will be, at best, minor blips in the nation’s $2.7 trillion health system." Yet there never was any evidence to back up these grandiose claims. Indeed, in its cost estimates for the legislation, the Congressional Budget Office (CBO) never assigned anything more than relatively trivial savings to the ACO concept.[1] Moreover, critics noted during the law’s consideration and shortly after its enactment that structural flaws would prevent ACOs—at least as conceived in the PPACA—from ever having a meaningful impact on the delivery system or on cost growth. But that did not stop the relentless hype by the law’s advocates. More than three years after enactment, it is clear that the ACOs of the PPACA variety will be, at