The film released in the United States on May 25, 2012.
Boris the Animal (Jemaine Clement), last of the Boglodite race, escapes from lunar prison. He wants vengeance on Agent K (Tommy Lee Jones), who shot off his left arm and jailed him. Boris flees from K and his partner Agent J (Will Smith), telling K that he is "already dead." K refuses to reveal details of his past with Boris, so J searches the MIB database. J finds murders by Boris, and that K deployed an 'ArcNet' in July 1969 that protected Earth from invading Boglodites, thus starving them to extinction. More details are classified, and Agent O (Emma Thompson), Chief Zed's replacement, stonewalls J with the same answer as K. That night, K vanishes, and only J remembers. O shows J a statue to K, killed by Boris in 1969. J learns his chocolate milk craving is a result of a 'temporal fracture'. At this point, the Boglodites invade Earth. J learns that Boris time-jumped to July 16, 1969, killed K, and prevented ArcNet from being installed.
J jumps off a skyscraper with another time travel device in order to travel back to July 15, 1969 and save K. In 1969, J meets 1969 K (Josh Brolin), 29 years old, light-hearted, flirting with 1969 O (Alice Eve). Whatever changed him "has not happened yet". K puts J inside a giant neuralyzer until J admits the truth, leaving out that K could die. The two follow clues to Griffin (Michael Stuhlbarg), a fifth-dimensional being who sees multiple timelines simultaneously. At The Factory studio party hosted by Andy Warhol aka Agent W, Boris attacks. Griffin flees, after promising a gift and a miracle game. Out of clues, K insists on pie and conversation. J remembers a miracle game that will take place soon at Shea Stadium. There, Griffin shares his timeline vision of "his favorite moment in human history", when the losing NY Mets win the World Series. Before Griffin can give them the ArcNet, he is kidnapped by the 1969 Boris. J and K pursue on high-powered monocycles. K recovers Griffin, who had been hiding the ArcNet under his hat. 1969 Boris escapes and argues with 2012 Boris, who criticizes "every mistake I've ever made, just waiting to happen".
J, K, and Griffin jet-pack to Cape Canaveral, Florida, where Apollo 11 prepares to launch moon-ward. J and K race to attach ArcNet to the rocket tip where it can automatically deploy once in space, but are stopped by military police. Griffin insists they tell the truth, and they finally persuade a skeptical colonel by showing him how important the agents are. Griffin stays on the ground. When J asks if they will meet again, he answers "anything is possible".
When the agents climb to the top of the rocket supports, both 1969 Boris and 2012 Boris attack them. J defeats 2012 Boris, using the time travel to predict his shots. K shoots off the left arm of 1969 Boris, who also falls. K retrieves and places ArcNet. K and J run a safe distance from the launch, and 2012 Boris is incinerated by the rocket exhaust. Apollo 11 lifts off, and ArcNet activates. 1969 Boris shoots the colonel dead, but is blown apart by K; J said to kill Boris this time, thus allowing the original timeline to be restored and remain safe from 2012 Boris's interference. A young boy, James, steps out of a nearby military vehicle, no doubt driven by his father, the colonel, looking for him. To J's surprise, the little boy pulls out a stopwatch similar to the one that he carries. K struggles with the idea of telling the boy what happened to his father, so he neuralyzes and comforts James, telling him, "Your daddy is a hero". J, hiding nearby, realizes that the boy is his younger self, and K was his surrogate father.
J returns to 2012, joins K alive at a diner for pie, and subtly thanks him for all his care; he also learns the future is only different just by the complete extinction of the Boglodites. Griffin, unseen on a nearby stool, says "this is my new favorite moment; unless K leaves without tipping and a meteor falls to Earth." K returns to tip and disaster is averted as a satellite collides with the meteor. Griffin sighs "That was a close one".
- Will Smith as Agent J
- Tommy Lee Jones as Agent K
- Josh Brolin as 1969 Agent K
- Jemaine Clement as Boris the Animal
- Emma Thompson as Agent O
- Michael Stuhlbarg as Griffin
- Mike Colter as Colonel James Darrell Edwards II.
- Nicole Scherzinger as Lilly Poison, Boris' girlfriend
- Michael Chernus as Jeffrey Price
- Alice Eve as 1969 Agent O
- David Rasche as Agent X
- Will Arnett as Agent Double A
- Keone Young as Mr. Wu
- Bill Hader as Agent W
- Cayen Martin as 1969 James Darrell Edwards III
- Feature on the 2012 Moviepedia Film Guide
- The Men in Black Wiki
- Men in Black Aliens on The Aliens Wiki
In 2009, following the success of the first movie and it's sequel (which made a combined $1.03 billion), Sony began to work on a third film. By February 2011, the production of the film was pushed back another 2 months for the second time as a result of ongoing script issues.  When production resumed, the crew began shooting a film that didn't have an ending. Rick Baker said, “It was a crazy production. We had a writer actually on the soundstage writing the words moments before the guys had to say them. I don’t think that’s any way to make a movie. But I’ve seen a rough cut and I was actually shocked at how good it was.”  The budget of the film ended up reaching a whopping $215 million, which apparently increased as a result of Will Smith's personal demands, which included an over-sized trailer and the re-shooting of scenes. It's also been reported that Smith accidentally revealed that Lady Gaga will appear in the film.  After all of these problems, people have expressed concern. However, opinions of the film have turned good after previews and props seen at Comic-Con.
- Michael Bay expressed interest in directing.
- Screenwriter David Koepp, who was originally involved with Men in Black II but left to write Spider-Man, signed on permanently for this film.
- Sacha Baron Cohen was considered for the role of Boris
- Betty White was originally rumored to have a role.
- This is Will Smith's first film in 3.5 years, since the release of Seven Pounds in December 2008. This is the longest he has gone without appearing in a movie since his film career started in 1993.
- Gemma Arterton was originally cast as young Agent O but scheduling conflicts prevented Arterton from taking the role.
- Josh Brolin plays a younger version of Tommy Lee Jones's character Agent K. Brolin's wife Diane Lane appeared with Jones in Lonesome Dove (1989) (TV). In the sequel, Streets of Laredo (1995) (TV), Lane's role was taken over by Sissy Spacek, who played Tommy Lee Jones's wife in Coal Miner's Daughter and is the cousin of cast member Rip Torn. Both Josh Brolin and Tommy Lee Jones stared in the 2007 film No Country for Old Men although their characters do not meet in the film.
- The previous film Men in Black II released the same year as Spider-Man. This film, the sequel, releases ten years later; the same year as the reboot The Amazing Spider-Man.
- This is the second threequel Steven Spielberg produced that involves Apollo 11 in its storyline. The first was Transformers: Dark of the Moon which focused on a Transformer ship discovered by Apollo.
- According to the trailer Agent J travels from 2012 to 1969, 43 years into the past. He wakes up and sees a young Agent K, played by Josh Brolin. Brolin is only 21 years and 5 months younger than Tommy Lee Jones, who plays the older Agent K. Brolin is also only seven months older than Will Smith.
- Yuri Lowenthal, who voices Knuckles the graffiti alien, had voiced Ben Tennyson in the Ben 10 cartoons; the Tennyson family is connected to the Plumbers, an organization similar to the Men in Black.