Super Mario Bros. 3 (スーパーマリオブラザーズ3, Sūpā Mario Burazāzu Surī) is a platform video game developed and published by Nintendo for the Nintendo Entertainment System (NES), and is the third game in the Super Mario series. The game was released in Japan in 1988, in the United States in 1990, and in Europe in 1991. Development was handled by Nintendo Entertainment Analysis and Development, led by Shigeru Miyamoto, who directed the game along with Takashi Tezuka.

The game focuses on Mario and his brother Luigi, who embark to a quest to save Princess Peach and the rulers of seven different kingdoms from the series' primary antagonist, Bowser, and his children, the Koopalings. The two must traverse a total of eight separate regions in order to restore order to the Mushroom World. Super Mario Bros. 3 builds on the gameplay of previous Mario games by introducing new power-ups used to augment character abilities, establishing several conventions that have also been featured in later titles of the franchise.

Prior to its North American release, gameplay footage from Super Mario Bros. 3 appeared in the Universal Studios film The Wizard, which helped to fuel anticipation amongst fans. The game was an instant commercial success, ultimately becoming one of the best-selling video games of all time. Super Mario Bros. 3 was also well received by critics and has ranked highly in numerous "greatest games of all time" lists. The title's popularity resulted in a short-lived animated television show, and it has since been ported to several of Nintendo's later consoles – notably as part of Super Mario All-Stars for the SNES, which featured an updated version that would also subsequently be used for Super Mario Advance 4.

Super Mario Bros. 3 is a two-dimensional platform game in which the player controls the on-screen protagonist (either Mario or Luigi) from a third-person perspective. The game shares similar game mechanics with previous titles in the series—Super Mario Bros., Super Mario Bros.: The Lost Levels, and Super Mario Bros. 2—but introduces several new elements. In addition to the running and jumping moves found in past games, the player can fly and float with the aid of special items, slide down slopes, and execute new types of jumps.Super Mario Bros. 3 is set after the events of previous games. Mario and Luigi embark on a mission on behalf of Princess Toadstool to stop Bowser and his children—the Koopalings—from terrorizing the kings of seven regions in the Mushroom World. The Koopalings stole the kings' magic wands and transformed them into animals. Each region serves as a game world that is divided into stage levels, and an eighth region is included as the final world, Dark Land. The eight worlds feature distinct visual themes; for example, the second world, "Desert Land", contains sand-covered levels with pyramids, while the levels in the fourth world, "Giant Land", are populated with obstacles and enemies four times as large as other worlds.

The player navigates through the game via two game screens: an overworld map and a level playfield. The overworld map displays an overhead representation of the current world and has several paths leading from the world's entrance to a castle. Paths connect to action panels, fortresses and other map icons, and allow players to take different routes to reach the world's goal. Moving the on-screen character to an action panel or fortress will allow access to that level's playfield, a linear stage populated with obstacles and enemies. The majority of the game takes place in these levels, with the player traversing the stage by running, jumping, and dodging or defeating enemies.

Completing stages allows the player to progress through the overworld map and to succeeding worlds. Each world features a final stage with a boss to defeat; the first seven worlds feature an airship controlled by one of the Koopalings, while the player battles Bowser in his castle in the eighth world. Other map icons include large boulders and locked doors that impede paths, and special minigames that provide the player a chance to obtain special power-ups. A new feature is the player's option to save power-up items obtained in minigames for later use via a menu accessible at the overworld screen.

In addition to special items from previous games like the "Super Mushroom" and "Fire Flower", new power-ups are introduced that provide the player with new options. Items vary in scarcity; for example, 1-up mushrooms, which give the player an extra attempt to play after the character dies, are abundant, while the "magic whistle", which enables the player to bypass certain worlds, only appears three times in the game. The "Super Leaf" and "Tanooki Suit" give Mario racoon and tanuki appearances respectively and allow him to fly or turn into stone to avoid enemies for a short period of time. Changing into a Tanooki statue while jumping would result in Mario pounding the ground and killing whatever enemies are directly under him, this marked the first appearance of the "Ground Pound" move in a Mario game, a move that would later be given to Yoshi in Yoshi's Island and that would later become part of Mario's standard moveset in Super Mario 64 and all subsequent games. Other suits include the "Frog Suit," which increases the character's underwater speed and agility and improves jumping height on land, and the "Hammer Suit," which gives Mario the appearance of the Hammer Bros. enemy and allows him to throw hammers at enemies and resist fire attacks. Some abilities provided by the suits are intended to give the player more navigation options in stages. For example, the Frog Suit allows the player to access underwater pipes, and the Tanooki Suit can temporarily transform Mario into an invincible statue, reducing the threat of damage. Additionally in level 5-3 Mario can gain a power-up known as the Kuribo's boot which allows him to stomp on spiked enemies and terrain, but which Mario loses at the end of the level.

Super Mario Bros. 3 includes a multiplayer option which allows two players to cooperatively play the game by taking turns at navigating the overworld map and accessing stage levels; the first player controls Mario, while the other controls Luigi. Through this mode, players can also access several minigames, including a remake of the original Mario Bros. arcade game, in which one player has the opportunity to steal the cards of another but may lose their turn if they lose the minigame.