Mario & Luigi: Bowser's Inside Story is a role-playing game where Mario and Luigi must navigate through the world inside Bowser's body. The brothers find themselves trapped inside Bowser's stomach, and their goal is to rescue each other and escape. Along the way, they meet various characters who aid them in their quest.
The gameplay involves exploration, battling enemies, and collecting items to progress through the story. Players can switch between Mario and Luigi to use their unique abilities, such as Luigi's jump attack and Mario's fire flower powers. The game also features turn-based battles against Bowser's minions.