Douglas Jay Feith (/ˈfaɪθ/; born July 16, 1953) is an American lawyer who served as Under Secretary of Defense for Policy from July 2001 until August 2005. He is a senior fellow at the Hudson Institute, a conservative think tank.

Feith has been described as an architect of the Iraq War. In the lead up to the war, he played a key role in promoting the false claim that the Saddam Hussein regime had an operational relationship with al-Qaeda (even though there was scant credible evidence of such a relationship at the time). A Pentagon Inspector General report found that Feith's office had "developed, produced, and then disseminated alternative intelligence assessments on the Iraq and al Qaida relationship, which included some conclusions that were inconsistent with the consensus of the Intelligence Community, to senior decision-makers."

Feith was born to a Jewish family in Philadelphia, Pennsylvania, one of three children of Rose (née Bankel) and Dalck Feith. His father was a member of the Betar, a Revisionist Zionist youth organization, in Poland, and a Holocaust survivor who lost his parents and seven siblings in the Nazi concentration camps. Dalck came to the United States during World War II and became a businessman, a philanthropist, and a donor to the Republican party.

Feith grew up in Elkins Park, part of Cheltenham Township, a Philadelphia suburb. He attended Philadelphia's Central High School, and later attended Harvard University, where he obtained his undergraduate degree and graduated magna cum laude in 1975. He continued on to the Georgetown University Law Center, receiving his J.D. magna cum laude in 1978. After graduation, he worked for three years as an attorney with the law firm Fried, Frank, Harris, Shriver & Jacobson LLP.

Feith worked on the staff of senator Henry M. Jackson in 1975 before going on to work on Elmo Zumwalt's campaign against segregationist senator Harry Byrd, Jr. Byrd, an independent since 1970, defeated Zumwalt, a Democrat, 57–38%.

At Harvard, Feith had studied under Richard Pipes, who joined the Reagan administration's National Security Council, in 1981, to help carry out a private intelligence project called Team B that Pipes and his students had conceived. Feith joined the NSC as a Middle East specialist that same year, working under Pipes.

He transferred from the NSC staff to the Pentagon, in 1982, to work as special counsel for Richard Perle, who was then serving as assistant secretary to the United States Secretary of Defense. Secretary of Defense Caspar Weinberger promoted Feith, in 1984, to deputy assistant secretary of defense for negotiations policy. When Feith left the Pentagon, in 1986, Weinberger awarded him the Department of Defense Medal for Distinguished Public Service, the department's highest civilian award.

During his time in the Pentagon in the Reagan administration, Feith helped to convince the Joint Chiefs of Staff, Weinberger and Secretary of State George Shultz all to recommend against ratification of changes to the Geneva Conventions. The changes, known as the "Additional Protocols," grant armed non-state actors prisoner of war status under certain circumstances even if they fail to distinguish themselves from the civilian population to the same extent as members of the armed forces of a high contracting party. Reagan informed the United States Senate in 1987 that he would not ratify Additional Protocol I. At the time, both The Washington Post and The New York Times editorialized in favor of Reagan's decision to reject Additional Protocol I as a revision of humanitarian law that protected terrorists.