James Addison Baker III (born April 28, 1930) is an American attorney, diplomat and statesman. A member of the Republican Party, he served as the 10th White House Chief of Staff and 67th United States Secretary of the Treasury under President Ronald Reagan and the 61st U.S. Secretary of State before returning as the 16th White House Chief of Staff under President George H. W. Bush.

Born in Houston, Baker attended The Hill School and Princeton University before serving in the United States Marine Corps. After graduating from the University of Texas School of Law, he pursued a legal career. He became a close friend of George H. W. Bush and worked for Bush's unsuccessful 1970 campaign for the United States Senate. After the campaign, he served in various positions for President Richard Nixon. In 1975, he was appointed Under Secretary of Commerce for Gerald Ford. He served until May 1976, ran Ford's 1976 presidential campaign, and unsuccessfully sought election as the Attorney General of Texas.

Baker ran Bush's unsuccessful campaign for the 1980 Republican presidential nomination, but made a favorable impression on the Republican nominee, Ronald Reagan. Reagan appointed Baker as his White House Chief of Staff, and Baker remained in that position until 1985, when he became the Secretary of the Treasury. As Treasury Secretary, he arranged the Plaza Accord and the Baker Plan. He resigned as Treasury Secretary to manage Bush's successful 1988 campaign for president. After the election, Bush appointed Baker to the position of Secretary of State. As Secretary of State, he helped oversee U.S. foreign policy during the end of the Cold War and dissolution of the Soviet Union, as well as during the Gulf War. After the Gulf War, Baker served another stint as White House Chief of Staff from 1992 to 1993.

Baker remained active in business and public affairs after Bush's defeat in the 1992 presidential election. He served as a United Nations envoy to Western Sahara and as a consultant to Enron. During the Florida recount following the 2000 presidential election, he managed George W. Bush's legal team in the state. He served as the co-chairman of the Iraq Study Group, which Congress formed in 2006 to study Iraq and the ongoing Iraq War. He serves on the World Justice Project and the Climate Leadership Council. Baker is the namesake of the James A. Baker III Institute for Public Policy at Rice University.