"Ben 10/Generator Rex: Heroes United" is an extended crossover special between Ben 10: Ultimate Alien and Generator Rex. It takes the form of an extended episode of Generator Rex, with it having an appearance of Ben Tennyson from Ben 10: Ultimate Alien and it being written by Man of Action, the creator of both animated series. Heroes United aired on November 25, 2011, on Cartoon Network, taking up a one-hour time block.

As a special event, it premiered at New York Comic Con 2011. Heroes United was universally acclaimed by fans of both series, and has hit the top 100 on iTunes.

This special is the second Cartoon Network crossover after the 2007 crossover special, The Grim Adventures of the KND. The events of the crossover specials take place during the third and final season of Generator Rex, and during the third and final season of Ben 10: Ultimate Alien.