Mario Kart Wii is a 2008 kart racing game developed and published by Nintendo for the Wii. It is the sixth installment in the Mario Kart series, and was released in April 2008. In Mario Kart Wii, the player takes control of one of 24 Mario series characters, who participate in races on 32 different race tracks using specialized items to hinder opponents or gain advantages.

Mario Kart Wii features multiple single-player and multiplayer game modes including two- to four-person split screen. Online multiplayer was supported until the discontinuation of Nintendo Wi-Fi Connection in May 2014. Mario Kart Wii features a returning multiplayer mode: Battle Mode. The aim is to defeat the other players by attacking them with power-ups, destroying balloons that surround each kart. Mario Kart Wii uses the Wii Remote's motion-controls to provide intuitive and conventional steering controls. Each copy of the game was bundled with the Wii Wheel accessory to augment this feature and mimic a steering wheel.

Development of Mario Kart Wii began shortly after the release of 2005's Mario Kart DS. Hideki Konno, who originally served as producer of the previous two games of the Mario Kart series, returned to produce the title. In his Nintendo composer debut, Ryō Nagamatsu joined Asuka Hayazaki (who composed 2005's Yoshi Touch & Go) as Mario Kart Wii's main composers. Both used new interpretations of the familiar melodies from earlier games alongside original material to create Mario Kart Wii's soundtrack.

Mario Kart Wii was received positively by critics and general audiences. Praise focused on the online mode, characters, innovative gameplay, tracks, and karts, whereas criticism was directed at its item balancing and rubber-band difficulty adjustment. It was a commercial success, selling more than five million copies in 2008 to become the best-selling game of the year. In total, Mario Kart Wii sold over 37 million copies, making it the second best-selling Mario Kart game after Mario Kart 8 Deluxe and one of the best-selling video games of all time.

Mario Kart Wii is a kart racing game featuring single-player and multiplayer modes. The players control one of many selectable Mario franchise characters and participate in races or battles using go-karts or motorbikes on courses thematically based on locations from the Mario franchise. During gameplay, the player views the action from a third-person perspective that tracks the player from behind their vehicle. Mario Kart Wii supports four different control schemes; the primary control scheme is the Wii Remote, optionally used in conjunction with the plastic Wii Wheel accessory, which uses the controller's motion-controls to simulate operating a steering wheel. The other supported control schemes are the Wii Remote with the Nunchuk attachment; the Classic Controller; and the GameCube controller, all of which allow the player to instead steer using the respective controllers' analog stick. While driving, the player collects power-ups from item boxes placed in various points on the track—these power-ups allow the player to attack opponents, causing them to slow down or spin out of control; defend against such attacks; or gain boosts in speed.

Mario Kart Wii features 24 playable characters from the Mario series, the largest roster of any Mario Kart game until the release of Mario Kart 8 in 2014. Wii introduces Baby Peach, Baby Daisy, Rosalina, Funky Kong, and Dry Bowser as playable drivers for the first time in the Mario Kart series. Unlike Mario Kart DS, where characters can drive a kart exclusive to that character and the standard go-kart, each character is assigned to one of three different weight classes, which affects the selection of vehicles the character can drive. Mario Kart Wii uses two different classes of vehicles, Karts and Bikes, with the latter being a new addition to the series. Bikes were also subdivided further into two categories: regular and sports bikes, with sports bikes featuring an alternate drift type known as inside drifting. Mii characters saved in the console's Mii Channel are also playable. Thirty-six vehicles are available in Mario Kart Wii, each of which has different properties that affect how the vehicle handles while driving. Half the characters, vehicles, and courses are initially unavailable to the player; certain objectives must be completed to unlock each one.

The game features eight cups—sets of four different tracks—for a total of 32 unique tracks. Like its predecessor Mario Kart DS, Mario Kart Wii has 16 new courses and 16 courses from prior Mario Kart games.

Mario Kart Wii features multiple game modes: Grand Prix, Time Trials, Versus, and Battle. All modes support single-player gameplay; Versus and Battle support local multiplayer for up to four players, with or without computer-controlled players. In Grand Prix, the player participates in four three-lap races from one of eight cups against eleven opponents. The player is awarded points at the end of each race based on their ranking. The total number of points collected, among other factors, determines the player's overall rank. Versus mode is similar to Grand Prix, but the presented courses and items are configurable. In Time Trials, the player must quickly complete the race in the fastest time possible—there are no opponents or items except for three Mushrooms given at the start of each race. The player can compete against a ghost character, which mimics a player's movements from an earlier race.