Motocross (often shortened to (MX) or MotoX) is a form of motorcycle racing or all-terrain vehicle racing held on enclosed off-road circuits and is widely considered the world’s most popular form of motorcycle racing.

Motocross tracks are often quite large (around 1 to 2 miles) and incorporate natural terrain features with varying amounts of man made jumps and other features.

It is not unheard of for a Motocross track to be made up entirely of hills and turns with no jumps at all. In contrast Supercross is an entirely man made track, comprising almost exclusively of a wide array of jumps and typically held in an indoor stadium.

Due to the size of the track, motocross races typically include 40 racers, in contrast to Supercross where it is only practical to have about 25.

Solo machines have engines ranging from 50cc to 550cc.

The most common distinction between motocross machines is whether they have two-stroke or four-stroke engines. Originally all bikes were four-stroke (in the Pre-65 era), but as the two-stroke engine improved they became more popular with their domination of the sport in the 1970s, 80s and 90s. The two-stroke engine produced more power than a four-stroke engine of the same capacity (cc), however fuel had to be mixed with oil.

The object of the contest is to complete either a defined number of laps (usually three to seven for amateurs, more for professionals) or fixed time period (anything up to 40 minutes) first.

Motocross can be an entry sport for motorsport in general. Classes for children as young as 4 exist for competition on 50cc machines.