Bullet Bills are missile-like projectiles with menacing looks and arms that appear in the Mario series. They have been enemies of Mario since their debut in Super Mario Bros.. These enemies can be found throughout many of the classic Mario games and in newer games, where they have increasingly been items, mostly in the Mario Kart series. Ever since Super Mario 64, Bullet Bills have had the ability to home in on Mario, also like a missile. They are shot out of Bill Blasters, and are usually under Bowser's control. However, when players stand on or walk so close that they touch the Bill Blaster the Bullet Bills are shooting from, the Bill Blaster will not shoot the Bullet Bills.

In the game Mario Kart DS and Mario Kart Wii, the player can collect Bullet Bills as items. After activating the Bullet Bill, the player's entire kart will transform into a giant Bullet Bill, which will automatically rocket down the track, knocking over any enemies or projectiles in the player's way, similarly to the Chain Chomp from Mario Kart: Double Dash!!. It will only last for a limited time, which increases the farther behind the player is in the race, and can only be received by the racers in 6th-8th place in Mario Kart DS, and 8th-12th place in Mario Kart Wii.

It has been greatly praised due to its ability to rocket the player around the course, knocking any player it comes across without having to steer. However, this item can also be a curse at times. For example, when racing on many of the trickier, narrower courses, the Bullet Bill can occasionally steer the player right up to the edge of the track, just before it wears off. This can often lead to the player falling into an abyss.

Players who are under the effects of the Mega Mushroom can be knocked back by this item. However, players who are invincible, due to a Star, are not affected when a Bullet Bill collides with them.

Bullet Bills are also an obstacle in the Airship Fortress track in Mario Kart DS.

Bowser Jr.'s kart in Mario Kart: Double Dash!! takes the form of a Bullet Bill and is called the Bullet Blaster. There is also a bike for small-sized characters in Mario Kart Wii called the Bullet Bike, which also resembles a Bullet Bill.