The Mushroom Kingdom (Japanese:キノコ王国) is a fictional setting in the Super Mario Bros. video game series where most of the games take place. It is a monarchy and its head of state and ruler is either Princess Peach Toadstool (in most games), the Chancellor of the kingdom (in Super Mario RPG), or King Toadstool (in the Mario comics and movie). Its capital as set forth by Paper Mario is Toad Town.

King Bowser Koopa wants to marry and/or kidnap Princess Peach Toadstool so he can take over the Mushroom Kingdom.

There are many other kingdoms/countries in the Mario universe including Sarasaland (home of Princess Daisy), Kitchen Island (home of Wario), and Beanbean Kingdom (setting of Mario & Luigi: Superstar Saga).

Super Mario Bros. 3 takes place in the "Mushroom World", and the various kingdoms were ruled by independent kings. Some people equate World 1: Grass Land with the Mushroom Kingdom, but it's not clear what the precise relationship is. The instruction manual for the game states that King Bowser Koopa had taken over the Mushroom Kingdom, and that the Mushroom Kingdom is a gateway to the Mushroom World, but this is never elaborated upon in Super Mario Bros. 3 or in any other games. In the Mario comic books, King Toadstool is based on the King of Grass Land.

Mario and Luigi were delivered to the Mushroom Kingdom by a stork as children in Super Mario World 2: Yoshi's Island, though varying sources disagree as to what occurred afterwards.