Plot

Agent J: I'm looking for K, have you seen him? Sort of a surly, older gentleman, smiles like this...
[J makes a poker face]
Agent O: K's been dead for over forty years.

Alien: [hands J a device] Here, take this, and all you have to do is jump.
[J is at the top of the Chrysler Building]
Agent J: You want me to JUMP?
Alien: TIME jump!

Agent J kembali ke masa lalu, saat tahun-tahun pertama MIB di tahun1960an, untuk menghentikan alien dari upayanya membunuh Agent K dan merubah sejarah.

Cast
Will Smith as Agent J, a senior MIB agent
Tommy Lee Jones as Agent K, a senior MIB agent
Josh Brolin as Young Agent K
Jemaine Clement as Boris the Animal
Emma Thompson as Agent O, the head of MIB in present day
Alice Eve as Young Agent O
Michael Stuhlbarg as Griffin, an alien with precognitive powers
Nicole Scherzinger as Lily, Boris' girlfriend
David Rasche as Agent X, the head of MIB in 1969
Will Arnett as Agent AA, Agent J's partner after K's "death"
Lanny Flaherty as Obadiah Price
Bill Hader as Andy Warhol / Agent W
Michael Chernus as Jeffrey Price
Mike Colter as Colonel James Darrell Edwards Jr.
Cayen Martin as Young James Darrell Edwards III/Young Agent J
Arifa Sura Sembiring as Alien

Quote

Agent J: I know what you're thinking: MIB, 3-D, we're going to be blowing stuff up and all that. But that's not really what we're doing right now. We're here for one purpose, and for one purpose only: Just to let you know that I'm about to make 3-D look good.

Agent J: Who are we?
Agent K: We are no-one. Our mission is to monitor extraterrestrial activity on Earth.