On March 31, 2011, a little over a year after the Patient Protection and Affordable Care Act (PPACA) became law, the Centers for Medicare & Medicaid Services (CMS) released proposed regulations on the operation and structure of Accountable Care Organizations (ACOs).1 The proposed regulations create the Medicare Shared Savings Program (MSSP), which CMS will implement no later than January 1, 2012, in line with section 3022 of PPACA. The deadline for submitting comments on the proposed rule is June 6, 2011. These proposed regulations have far-reaching implications for new and existing health care organizations that want to participate in the MSSP as ACOs. CMS is seeking comments to determine which legal entities should qualify as ACOs, what the MSSP should require of its participants, and how the final MSSP should function. Click here for the full text of the rule.