THX 1138 is a 1971 science fiction film directed by George Lucas, from a screenplay by Lucas and Walter Murch. It depicts a dystopian future in which a high level of control is exerted upon the populace through omnipresent, faceless, android police officers and mandatory, regulated use of special drugs to suppress emotion, including sexual desire.

It was the first feature-length film directed by Lucas, and a more developed, feature-length version of his student film Electronic Labyrinth: THX 1138 4EB, which he made in 1967 while attending the University of Southern California, based on a one and a quarter page treatment of an idea by Matthew Robbins. The film was produced in a joint venture between Warner Brothers and Francis Ford Coppola's then-new production company, American Zoetrope. A novelization by Ben Bova was published in 1971.