The Louisiana Purchase Sesquicentennial half dollar was a proposed United States commemorative coin, legislation for which passed both houses of Congress, but was vetoed in 1954 by President Dwight Eisenhower. Intended to celebrate the 150th anniversary of the Louisiana Purchase (1803), the coin was lobbied for by both the Missouri Historical Society (MHS) and the Louisiana Purchase 150th Anniversary Association of New Orleans, who hoped to be able to buy the entire coin issue from the government and sell it at a profit.
Numismatist Eric P. Newman led the MHS's efforts, and corresponded with Congressman Thomas B. Curtis of Missouri, who helped push the bill forward with officials of the Louisiana group, such as Clay Shaw. Although many commemorative coins had been authorized by Congress in the 1930s, legislators passed few after that; the Treasury Department was strongly against their issue. When the House of Representatives held a hearing on the Louisiana Purchase Sesquicentennial half dollar, the bill was opposed by assistant director of the Mint F. Leland Howard. The House passed the bill in April 1953, but the Senate was slow to act, passing it in January 1954, and after the House concurred with the Senate amendments, the bill was sent to Eisenhower later that month.
Eisenhower vetoed the bill, as well as two other commemorative coin bills, on February 3, 1954. Congress made no attempt to override his vetoes. No commemorative coins were authorized or issued by the United States after 1954 until a new issue was struck in 1982.