The two federal agencies primarily responsible for administering the private health insurance provisions in the Patient Protection and Affordable Care Act (ACA)—the Centers for Medicare & Medicaid Services (CMS) within the Department of Health and Human Services (HHS), and the Internal Revenue Service (IRS) within the Treasury Department—have taken certain actions to delay, extend, or otherwise modify the law’s implementation. Table 1 summarizes selected administrative actions taken by CMS and the IRS to address ACA implementation. The table entries, which are grouped under general topic headings, are not organized in any particular priority order. Each entry includes a brief summary of the action and some accompanying explanatory material and comments to help provide additional context. Where available, links are provided to relevant regulatory and guidance documents online. Readers are encouraged to review these documents for more details about each action taken. This report is updated periodically to reflect significant ACA implementation actions taken by the Administration. A companion CRS report summarizes all the legislative actions taken by Congress since the ACA’s enactment to repeal, defund, delay, or otherwise amend the law.