William Scott Ritter Jr. (born 1961) is an American author, former United States Marine Corps intelligence officer, former United Nations Special Commission (UNSCOM) weapons inspector.

Ritter served as a junior military analyst during Operation Desert Storm. He then served as a member of the UNSCOM overseeing the disarmament of weapons of mass destruction (WMD) in Iraq from 1991 to 1998, from which he resigned in protest. He later became a critic of the Iraq War and United States foreign policy in the Middle East.

In February 2005, writing on Al Jazeera's website, Ritter wrote that the "Iraqi resistance" is a "genuine grassroots national liberation movement," and "History will eventually depict as legitimate the efforts of the Iraqi resistance to destabilize and defeat the American occupation forces and their imposed Iraqi collaborationist government."

Ritter's book Target Iran: The Truth About the White House's Plans for Regime Change was published in 2006. Nathan Guttman in his review for The Forward said Ritter accused the "pro-Israel lobby of dual loyalty and 'outright espionage'". Ritter said that Israel was pushing the Bush administration into war with Iran. He accused the pro-Israel lobby of invoking the Holocaust and of making false claims of antisemitism. Ritter told The Forward "at the end of the day, I would like to believe that most of American Jews will side with America."