BMX is a form of cycling on specially designed bicycles which usually have 20-inch wheels (smaller than the 26-inch wheels found on mountain bikes and the 700C or 27-inch wheels found on more conventional road racing bicycles). The sport includes races on sandy and hilly tracks—BMX racing—as well as the performances of tricks on flat ground, wooden ramps or obstacles found on the streets—BMX freestyle.

BMX originated in the state of California, United States in the late 1960s, when teenagers imitated their motocross heroes (most notably Steve McQueen) on their bicycles. Scot Breithaupt is credited as the founder of BMX. The 1971 motorcycle racing documentary "On Any Sunday" is generally credited with inspiring the movement nationally. In the opening scene, kids are shown riding their Schwinns off-road. It wasn't until the middle of that decade that the sport achieved critical mass, and manufacturers began creating bicycles designed specially for the sport. In the case of Freestyle BMX, it wouldn't be what it is today without Bob Haro's contribution. He merged skateboarding tricks with freestyle BMX which led to the current-day style of this extreme sport.

Via: WIkipedia
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