Harold Edward Holt (5 August 1908 – 17 December 1967) was an Australian politician who served as the 17th prime minister of Australia from 1966 until his presumed death in 1967. He held office as leader of the Liberal Party.

Holt was born in Sydney and moved to Melbourne in childhood, studying law at the University of Melbourne. Before entering politics he practised law and was a lobbyist for cinema operators. He was first elected to the House of Representatives at the age of 27, becoming a member of parliament (MP) for the division of Fawkner at a by-election in 1935. A member of the United Australia Party (UAP), Holt was made a minister without portfolio in 1939, when his mentor Robert Menzies became prime minister. His tenure in the ministry was interrupted by a brief stint in the Australian Army, which ended when he was recalled to cabinet following the deaths of three ministers in the 1940 Canberra air disaster. The government was defeated in 1941, sending the UAP into opposition, and he joined the new Liberal Party upon its creation in 1945.

When the Liberals came to office in 1949, Holt became a senior figure in the new government. As Minister for Immigration (1949–1956), he expanded the post-war immigration scheme and relaxed the White Australia policy for the first time. He was also influential as Minister for Labour and National Service (1949–1958), where he handled several industrial relations disputes. Holt was elected deputy leader of the Liberal Party in 1956, and after the 1958 election replaced Arthur Fadden as Treasurer. He oversaw the creation of the Reserve Bank of Australia and the decimal Australian dollar, but was blamed for a credit crunch that almost cost the Coalition the 1961 election. However, the economy soon rebounded and Holt retained his place as Menzies' heir apparent.

Holt became prime minister in January 1966, elected unopposed as Liberal leader following Menzies' retirement. He fought a general election later that year, winning a landslide victory. The Holt Government continued the dismantling of the White Australia policy, amended the constitution to give the federal government responsibility for indigenous affairs, and took Australia out of the sterling area. Holt promoted greater engagement with Asia and the Pacific, and made visits to a number of East Asian countries. His government expanded Australia's involvement in the Vietnam War, and maintained close ties with the United States under President Lyndon B. Johnson. While visiting the White House, Holt proclaimed that he was "all the way with LBJ", a remark which was poorly received at home.

In December 1967, Holt disappeared while swimming in rough conditions at Cheviot Beach, Victoria. He was presumed dead, although his body was never recovered; his disappearance spawned a number of conspiracy theories. Holt was the third Australian prime minister to die in office. He was succeeded by Country Party leader John McEwen on an interim basis and then by John Gorton. His death was commemorated in a number of ways, among them by the establishment of the Harold Holt Memorial Swimming Centre in Melbourne.