Potter Stewart (January 23, 1915 – December 7, 1985) was an American lawyer and judge who served as an associate justice of the United States Supreme Court from 1958 to 1981. During his tenure, he made major contributions to criminal justice reform, civil rights, access to the courts, and Fourth Amendment jurisprudence.

After graduating from Yale Law School in 1941, Stewart served in World War II as a member of the United States Navy Reserve. After the war, he practiced law and served on the Cincinnati city council. In 1954, President Dwight D. Eisenhower appointed Stewart to a judgeship on the U.S. Court of Appeals for the Sixth Circuit. In 1958, Eisenhower nominated Stewart to succeed retiring Associate Justice Harold Hitz Burton, and Stewart won Senate confirmation afterwards. He was frequently in the minority during the Warren Court but emerged as a centrist swing vote on the Burger Court. Stewart retired in 1981 and was succeeded by the first female United States Supreme Court justice, Sandra Day O'Connor.

Stewart wrote the majority opinion in notable cases such as Jones v. Alfred H. Mayer Co., Katz v. United States, Chimel v. California, and Sierra Club v. Morton. He wrote dissenting opinions in cases such as Engel v. Vitale, In re Gault and Griswold v. Connecticut. His concurring opinion in Jacobellis v. Ohio popularized the phrase "I know it when I see it."