Clarence Douglas Dillon (born Clarence Douglass Dillon; August 21, 1909 – January 10, 2003) was an American diplomat and politician who served as the United States ambassador to France from 1953 to 1957 and as the 57th United States secretary of the treasury from 1961 to 1965. He was also a member of the Executive Committee of the National Security Council (ExComm) during the Cuban Missile Crisis. His conservative economic policies while Secretary of the Treasury were designed to protect the U.S. dollar.

Dillon was born on August 21, 1909, in Geneva, Switzerland, the son of American parents, Anne McEldin (née Douglass) and financier Clarence Dillon. Although Dillon grew up as a patrician, his paternal grandfather, Samuel Lapowski, was a poor Jewish emigrant from Poland. After leaving Poland, his grandfather settled in Texas after the American Civil War and married Dillon's Swedish-American grandmother. Dillon's father later changed his family name to Dillon, an Anglicization of "Dylion", his grandmother's maiden name. Dillon's mother was descended from the Graham family, Lairds of Tamrawer Castle at Kilsyth, Stirling, Scotland.^{[citation needed]}

Dillon began his education at Pine Lodge School in Lakehurst, New Jersey. He continued at Groton School in Massachusetts, then at Harvard College, A.B. magna cum laude 1931 in American history and literature. Dillon earned a varsity letter for football his senior year.

In 1938, he became Vice-President and Director of Dillon, Read & Co., a firm that bore his father's name (Clarence Dillon). After his World War II service on Guam, on Saipan, and in the Philippines, he left the United States Navy as Lieutenant Commander decorated with the Legion of Merit and Air Medal. In 1946 he became chairman of Dillon, Read; by 1952 he had doubled the firm's investments.

Dillon had been active in Republican politics since 1934. He worked for John Foster Dulles in Thomas E. Dewey's 1948 presidential campaign. In 1951 he organized the New Jersey effort to secure the 1952 Republican nomination for Dwight D. Eisenhower. He was also a major contributor to Eisenhower's general election campaign in 1952.

President Eisenhower appointed him United States Ambassador to France in 1953. Following his return he became Under Secretary of State for Economic Affairs in 1958 before becoming Under Secretary of State the following year. TIME reported that if Richard Nixon had won the presidential election of 1960 that Dillon was to be chosen as Secretary of State.

In 1961, John F. Kennedy, appointed Republican Dillon Treasury Secretary. Dillon remained Treasury Secretary under President Lyndon B. Johnson until 1965. According to Richard Dean Burns and Joseph M. Siracusa, Dillon's leadership of the economic policy team, exerted significant conservative influence on the overall direction of the administration. He effectively convinced the president that the nation's main economic challenge was the balance of payments deficit, leading to the adoption of a moderate approach and the dismissal of more radical liberal solutions to domestic issues. President Kennedy's choice of Dillon as Secretary of the Treasury reflected a deep concern about the balance of payments deficit and the resulting "gold drain." By choosing Dillon, a Wall Street figure with strong Republican connections and a reputation for advocating sound monetary policies, Kennedy aimed to reassure the financial community, which was apprehensive about the potential loose monetary policies of the incoming Democratic administration. According to Theodore Sorensen, the president's choice was primarily influenced by the need to maintain global confidence in the dollar and prevent a massive conversion of dollars into gold. Kennedy shared Dillon's moderately conservative economic perspectives at the time of his appointment, and Dillon enjoyed close access to the president throughout his presidency. He was one of the few political associates who socialized with Kennedy as well.

The emphasis placed by Kennedy and Dillon on addressing the balance of payments issue had a substantial impact on the administration's overall economic policy, steering it toward conservatism. The growing annual deficits in dollar payments had led to a significant accumulation of dollars in the hands of foreign banks and governments. The recurring loss of confidence in the value of the dollar prompted foreign holders to exchange their dollars for American gold, which had a fixed value relative to the dollar. This "gold drain" raised concerns within the financial community and remained a prominent issue during both the Kennedy and Johnson administrations. In an effort to stabilize the status of the dollar and halt the outflow of gold, the Kennedy administration avoided economic measures that could potentially increase inflation and undermine foreign confidence in the dollar. During the initial years of Kennedy's presidency, Dillon's success in prioritizing the payments deficit prevented more aggressive fiscal and monetary interventions in the economy or increased spending on social programs.