Motocross (often shortened to MX or MotoX) is a form of motorcycle sport or all-terrain vehicle racing held on enclosed off road circuits. Motocross is derived from the French, and traces its origins to British Scrambling competitions. The name "motocross" is a portmanteau derived from the words "motorcycle" and "Cross Country".

The AMA Motocross Championship (the "outdoor series") season begins in early May and continues until mid-September, and consists of 12 rounds at 12 major tracks all over the continental United States. There are two classes; "Motocross" and "Motocross Lites" (formerly "250cc" and "125cc"). Each round has two motos of 30 minute-plus-two-laps, per class, held approximately two hours apart.

The Grand Prix (or Motocross World Championship) is predominantly held in Europe with some "flyaway" rounds, recently in South Africa and Japan, but over its history it has visited numerous countries including; Indonesia, Australia and countries on both American continents. There are two classes; MX1 and MX2 (analogous to "Motocross" and "Motocross Lites" respectively). Race duration is slightly longer at 35 minutes plus two laps, while the series is longer, generally incorporating over 16 rounds.

The annual Motocross des Nations (now called Motocross of Nations) is usually held at the end of the year when National and World Championship series have ended. The format involves teams of three riders representing their nations. Each rider competes in a different class (MX1, MX2 and "Open"). There are three motos with two classes competing per moto. The location of the event changes from year to year. The United States, Belgium and Great Britain have had the greatest success. France has had a very successful year in the last Motocross of nations.