Congress remains deeply divided over implementation of the Patient Protection and Affordable Care Act (ACA), the health reform law enacted in March 2010 during the 111th Congress. Since the ACA's enactment, lawmakers opposed to specific provisions in the ACA or the entire law have repeatedly debated its implementation and considered bills to repeal, defund, delay, or otherwise amend the law. Much of this legislative activity has taken place in the House, which reverted to Republican control in the 112th Congress (2011-2012). Since then, the Republican-led House has passed numerous ACA-related bills, including legislation that would repeal the entire law. There has been less debate in the Senate, which remained under Democratic control during the 112th and 113th Congresses. Most of the House-passed ACA legislation was not considered in the Senate during that period. However, with Republicans in control of both chambers in the 114th Congress (2015-2016), opponents of the ACA sought new opportunities to pass and send to the President legislation that would change the law. The House-passed legislation includes stand-alone bills as well as provisions in broader, often unrelated measures that would have (1) repealed the ACA in its entirety and, in some cases, replaced it with new law; (2) repealed, or by amendment restricted or otherwise limited, specific provisions in the ACA; (3) eliminated appropriations provided by the ACA and rescinded all unobligated funds; (4) replaced the ACA's mandatory appropriations with authorizations of (discretionary) appropriations, and rescinded all unobligated funds; or (5) blocked or otherwise delayed implementation of specific ACA provisions. Republican leaders also have used a special legislative process known as budget reconciliation in an effort to repeal parts of the ACA. On October 23, 2015, the House passed a reconciliation bill that would repeal several provisions of the ACA. The House-passed bill (H.R. 3762) was taken up by the Senate, which substituted its own more extensive set of ACA repeal provisions. The Senate approved H.R. 3762, as amended, on December 3, 2015. The House subsequently approved the Senate-passed bill. President Obama vetoed H.R. 3762 on January 8, 2016. The House failed to override the veto. A few bills to amend specific elements of the ACA that attracted sufficiently broad and bipartisan support have been approved by both the House and the Senate and signed into law. During the 111th Congress, a number of clarifications and technical adjustments to the ACA were enacted. Since then, several more substantive ACA amendments have become law. For example, Congress repealed Title VIII of the ACA-the Community Living Assistance Services and Supports (CLASS) Act-which would have established a voluntary, long-term care insurance program to pay for community-based services and supports for individuals with functional limitations. Lawmakers also repealed a tax-filing provision (IRS Form 1099) that had been included in the ACA, and, in two separate legislative actions, reduced the annual appropriations to the ACA's Prevention and Public Health Fund over the period FY2013-FY2024 by a total of $9.75 billion. In addition to considering ACA repeal or amendment in authorizing legislation, some lawmakers have used the annual appropriations process in an effort to eliminate funding for the ACA's implementation and address other concerns they have with the law. A companion report, CRS Report R44100, Use of the Annual Appropriations Process to Block Implementation of the Affordable Care Act (FY2011-FY2017), summarizes the ACA-related language added to annual appropriations legislation by congressional appropriators since the ACA was signed into law.