Men in Black 3 (stylized as MIB³) is a 2012 American science fiction action comedy film based on the Marvel Comics series of a similar name, in turn based on the conspiracy theory, which is the sequel to Men in Black II (2002), the third installment in the Men in Black film series and the final installment in the original trilogy. Directed by Barry Sonnenfeld and written by Etan Cohen, the film stars Will Smith, Tommy Lee Jones and Josh Brolin, with Jemaine Clement, Michael Stuhlbarg, Bill Hader and Emma Thompson in supporting roles. In the film, James Darrell Edwards III / Agent J (Smith) is required to go back in time to prevent the assassination of his partner Kevin Brown / Agent K (Jones and Brolin), the fallout of which threatens the safety of Earth.

Produced by Columbia Pictures and Amblin Entertainment in association with Parkes+MacDonald Image Nation and Hemisphere Media Capital, and distributed by Sony Pictures Releasing, development of the sequel began during filming of its predecessor, with its premise suggested by Smith to Sonnenfeld. Despite rumors of a fallout between Smith and Sonnenfeld during the filming of Men in Black II, their returns were confirmed alongside Jones by May 2010, after being announced the previous year. David Koepp and Jeff Nathanson were later hired to perform uncredited rewrites to Cohen's original screenplay and principal photography began that November.

Filming was split into two parts, first occurring between November and December 2010, and restarting between April and June 2011, taking place primarily in New York City. Composer Danny Elfman, who scored the previous two installments, returned to score the third. With an officially acknowledged production budget of $215 million, it is one of the most expensive films ever made.

Men in Black 3 first premiered at O2 World in Berlin on May 14, 2012, and was theatrically released in the United States on May 25. It received generally positive reviews from critics, with praise for the performances of the cast (particularly Brolin's), and was considered an improvement over its predecessor. The film grossed $654.2 million worldwide, becoming the tenth-highest grossing film of 2012 and the highest grossing film in the franchise, unadjusted for inflation. A standalone sequel, Men in Black: International, was released in 2019, without most of the original cast.