The fighting words doctrine, in United States constitutional law, is a limitation to freedom of speech as protected by the First Amendment to the United States Constitution.

In 1942, the U.S. Supreme Court established the doctrine by a 9-0 decision in Chaplinsky v. New Hampshire. It held that "insulting or 'fighting words,' those that by their very utterance inflict injury or tend to incite an immediate breach of the peace" are among the "well-defined and narrowly limited classes of speech the prevention and punishment of [which] ... have never been thought to raise any constitutional problem