Motocross racing is form of motorcycle or ATV racing held on artificial loose dirt circuits, constructed with many corners and steep bumps from which riders launch themselves high into the air.

Motocross motorcyles are lightweight and powered by highly tuned two-stroke or four-stroke engines (but usually geared for quick acceleration rather than very high speeds). They have knobby tyres for traction on loose surfaces, a highly absorbent suspension designed to cope with the shock of heavy landings, and short gearing designed for swift acceleration rather than the ultimate in top speed. Unusually for racing machines, they can be purchased in a ready-to-race condition at moderate prices from major motorcycle manufacturers. As of November 2004. A 250cc two-stroke motorcross machine from Honda, a large Japanese manufacturer, has a list price of approximately 6000 USD. Professional riders, however, modify their machines further, both for outright performance and to have the bike's behaviour more in tune with their own preferences. The latest trend in motocross motorycles is towards four-stroke engines. Honda, Yamaha, Kawasaki and Suzuki have all developed four-stroke engines that rival the two-strokes in both weight and power and are significantly easier to use due to the smoother power delivery. These engines have been developed due to environmental concerns regarding the increased emissions of two-strokes. Some predict that two-strokes will not be available to buy after 2007, perhaps earlier in states such as California.

The object of the contest is to complete a defined number of laps (usually three to five) the quickest. This competition is called a moto. Usually a race consists of two motos with the scores combined for an overall result.

Motocross racing is one of the most visually appealing forms of motorsport, with riders performing seemingly death-defying leaps, turns visibly at the edge of traction (as indicated by a sliding, spinning rear tyre throwing dirt at all behind it), and the effort of riders clearly visible as the move their bodies around their motorcycles to balance the bikes for maximum speed. Capitalising on this appeal, two variants called supercross and arenacross have evolved, held on tighter tracks in sports stadiums (even indoors) with more, even higher jumps.

ATV's are enjoying a recent increase in popularity in the motocross scene. Due to a several ATV injuries and a number of high profile lawsuits, from 1989 to 1999 there was virtually no factory support for racing. The Yamaha Banshee was the only sport quad produced for that decade, and it received no updates either. For that decade, most quad racers purchased used Honda 250R's, a 250cc two-stroke race quad that Honda produced during the late eighties, ending production in 1989 to comply with a 10 year moratorium on sport quads, agreed upon by the major Japanese manufacturers. In 1999 Honda reentered the sport scene with a four-stroke quad, the 400EX. While not as fast and light as the 250R, with time and money it could be built into a formidable race quad. The 400EX began to dominate racing for the next five years until Yamaha released the YFZ450, a 450cc quad designed specifically for race use. The YFZ450 was immediately the best quad to buy for racing, as it could be very competitive straight off the factory floor. Eight months later Honda released their competition to the YFZ450, the TRX450R, another race ready stock bike for similar money.

Sidecarcross has been around since the 50’s but has declined in popularity since the 90’s. This variant is common in Europe, with a few followers in USA, New Zeeland and Australia. Motocross sidecars are purposebuilt frames that resemble an ordinary motocross-cycle with a flat platform to stand on attached to either side and a handlebar at waistheight to hold on to. The passenger balances the bike by being a counterweight, especially in corners and on jumps. It’s driven on ordinary crosstracks. It is very physically demanding, especially for the passenger.

The major framebuilders today (2004) are VMC, BSU, AYR, EML and Woodenleg. Ordinary engines can be used, but size matters and two engines purposebuilt for sidecars exist, Zabel (Germany) and MTH (Austria) are most common. Fourstrokes are getting more common, usually KTM(Austria).

Freestyle motocross, a relatively new sport, shuns racing and concentrates on performing acrobatic stunts while jumping these motorcycles.

Many children are introduced to motorcycling through miniature motorcross bikes, some as young as 4 or 5 years old riding tiny 50cc machines. Most professional motorcycle racers from North America and Australia began their racing career on such machines; European motorcycle racers typically begin in pocketbike racing.

de:Motocross