Teenage Mutant Ninja Turtles III: The Manhattan Project, released as Teenage Mutant Ninja Turtles 3: The Manhattan Project (ティーンエイジ・ミュータント・ニンジャ・タートルズ2 ザ・マンハッタン・プロジェクト) in Japan, is a side-scrolling beat-'em-up released by Konami for the Nintendo Entertainment System in North America in 1992. It is the third video game iteration of the Teenage Mutant Ninja Turtles franchise for the NES. The game features the same play mechanics featured in the previous game, Teenage Mutant Ninja Turtles II: The Arcade Game, but unlike its predecessor, it is an original title for the NES without any preceding arcade version. The Japanese version was released a few months prior to the North American release, and a number behind that release due to the name change of the original Teenage Mutant Ninja Turtles game for the NES when it was released for the Japanese market.

TMNT III can be played by up to two players simultaneously, with each player controlling a different character. The player can choose between any of the four turtles: Leonardo, Raphael, Michaelangelo, and Donatello, each wielding their signature weapon. Two different 2-player modes are featured in the game, the first mode allows both players to hurt each other with their attacks, while the other mode disables this feature. The player has a limited number of lives that gets depleted every time the player's energy gauge runs out. If one player has run out of lives, they can use the remaining ones from the other player's remaining stock (this is possible to do in the 1-player mode as well). The player is allowed to change their character every time they lose life. Up to three chances to continue are provided.

The controls are mostly unchanged from the second NES game, with one attack button and one jump button. The turtles can now perform a toss attack against their enemies by holding the d-pad downwards while pressing B. Each turtle also has a different special attack that is performed by pressing B and A simultaneously. Every time the player performs this attack, a portion of their energy will be lost, unless they are on their last bar of life.

The game is composed of a total of eight levels, spanning from the beaches of Florida to the floating island of Manhattan to the Technodrome, ultimately concluding with Shredder's lair. The game's regular enemies include a variety of Foot Soldiers, as well as Giant Mousers and Stone Warriors. The game's bosses include villains from the cartoon series and toyline such as Dirtbag, Groundchuck, Slash, and Leatherhead, in addition to the return of Shredder and Krang, along with Bebop and Rocksteady. Tokka and Rahzar from the film Teenage Mutant Ninja Turtles 2: The Secret of the Ooze also appear, alongside Shredder's mutated counterpart from the film, Super Shredder, as the game's final boss.

Despite the fact that the cover art features the Turtles fighting a Triceraton, no Triceratons appear in the game.