Codename: Kids Next Door[c] is an American animated television series created by Mr. Warburton for Cartoon Network.

The series follows the adventures of a diverse group of five children who operate from a high-tech treehouse, fighting against adult and teenage tyranny with advanced 2×4 technology.

[5] A special half-hour crossover episode with fellow Cartoon Network series, The Grim Adventures of Billy & Mandy, aired in 2007.

Codename: Kids Next Door has also appeared in DVD anthologies and compilation video games from Cartoon Network.

The series revolves around a group of five 10-year-old children (later retconned to be varying ages), using codenames Numbuhs 1 through 5, who are the main home operatives of what is known as Sector V, which is part of a worldwide espionage-style organization called the Kids Next Door.

Following a period of training, every member of the Kids Next Door chooses a number or alphanumeric code (deliberately pronounced and spelled as "Numbuh") and is sent to a "sector" that acts as their home base.

[7][8] KND agents utilize a vast array of mechanical, electronic gadgets, weapons, and machinery, collectively referred to as 2×4 (two-by-four) technology.

However, as the series progressed, the kind of objects their technology was constructed from became bigger, consisting of things such as large vehicles and small buildings.

Not only that, but the complexity of their technology, such as their defensive weaponry and means of transportation, advanced to such absurd levels as to be considered science fiction, despite all of it still being constructed from nothing but an assortment of objects.

Warburton created a pilot episode, titled "Diseasy Does It", for another planned show, Kenny and the Chimp, which was to be produced by Hanna-Barbera.

[12] Codename: Kids Next Door was the most popular TV series produced at Curious Pictures, who previously did the work on Sheep in the Big City at Cartoon Network.

Four episodes were also released on the Game Boy Advance Video cartridge Codename: Kids Next Door, Volume 1.

Also, in the MAD episode "Taking Nemo / Once Upon a Toon", Numbuh One makes a cameo as one of the cartoon characters who have forgotten his identity.

The characters are also featured in the books 2x4 Technology Handbook and Sooper Secrets and Boomerang Bloopers, both by Benjamin Alison Wilgus.

The characters appeared in a one-shot tie-in for Cartoon Network and IDW's Super Secret Crisis War crossover comic in 2014.

In Cartoon Network Universe: FusionFall, Numbuhs One through Five, and villains Father, Toiletnator, and Stickybeard appear as non-playable characters.

In Cartoon Network: Punch Time Explosion, Father and Numbuh 1 are playable, Sector V Treehouse and the C.O.O.L.-B.U.S.

[33] Following having no response, Warburton eventually decided to create a pitch that would be distributed over the internet pseudonymously to try and get the series approved with help from fans.

[36] On April 1, 2015, a fan-made petition was started on Change.org to make G:KND a real series, was signed by Warburton himself and Dee Bradley Baker.

[37] Warburton later noted that the executives at Cartoon Network had noticed the response but were not interested in a continuation to KND, though he remained confident to get the sequel approved in the future.