The Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (MMA) is a landmark federal law in the United States that significantly reformed the Medicare program, creating Medicare Part D for prescription drug coverage. This represented the largest expansion of Medicare since its inception in 1965. Enacted during the 108th Congress under President George W. Bush, the legislation introduced a voluntary prescription drug benefit aimed at providing affordable access to medications for seniors and individuals with disabilities. It also modernized other aspects of Medicare, including enhancements to Medicare Advantage (Part C) plans and adjustments to traditional Medicare Part B. The act was passed by the House of Representatives on November 22, 2003 (220-215) and by the Senate on November 25, 2003 (54-44), before being signed into law on December 8, 2003. Implementation of the prescription drug benefit began on January 1, 2006. The MMA's passage was highly contentious, reflecting partisan divides over the role of government in healthcare and the involvement of private insurers. Republicans championed it as modernizing Medicare with market-based reforms, while Democrats criticized it for favoring pharmaceutical and insurance industries, prohibiting direct government negotiation of drug prices, and adding substantial costs to the federal budget—estimated at over $500 billion in its first decade. The legislation created a complex structure for Part D, where beneficiaries enroll in private standalone drug plans or Medicare Advantage plans with drug coverage, subsidized by the government. Over time, the program has covered millions of enrollees, reducing out-of-pocket drug costs, but it has faced ongoing debates regarding its efficiency, coverage gaps like the 'donut hole' (later addressed by the Affordable Care Act), and the influence of pharmaceutical lobbying. Beyond prescription drugs, the MMA included provisions for rural health access improvements, demonstration projects for chronic care management, and income-related premium adjustments. It represented a shift toward greater privatization in Medicare, empowering private entities to administer benefits. The act's legacy endures in the structure of American healthcare, with Part D now serving over 50 million beneficiaries, though it continues to be scrutinized for its fiscal impact and effectiveness in controlling drug prices.