On January 1, 2015, 89 new Medicare Accountable Care Organizations (ACOs) began participating in the Medicare Shared Savings Program (MSSP). In its announcement about the new ACOs, the federal Centers for Medicare & Medicaid Services (CMS) noted that there are now a total of 424 ACOs in operation. The 89 new ACOs serve beneficiaries in 40 states. About a quarter will operate in two or more states, including one new ACO that will serve beneficiaries in eight states. According to CMS, with the launch of operations by the 89 new ACOs, the number of beneficiaries attributed to MSSP ACOs has . . .