Mountain biking usually refers to the sport of riding bicycles possessing particular design characteristics for off-road, although sometimes the term simply refers to riding a mountain bike, which can be done almost anywhere. The sport requires endurance, bike handling skills and self-reliance. It is an individual sport which can be performed almost anywhere.

Because riders are often far from civilization, there is a strong ethic of self-reliance in the sport. Riders must learn to repair their broken bikes or flat tires to avoid being stranded miles from help. This reliance on survival skills accounts for the group dynamics of the sport. Club rides and other forms of group rides are common, especially on longer treks.

Mountain biking is roughly broken down into five categories: cross country, downhill, Freeride, Dirt Jump and trials/street riding. However, most mountain bikes have a similar look: knobbly tires, large round frame tubing, and some sort of suspension or shock absorbers are the usual pieces of equipment. Mountain biking can be done anywhere from a back yard to a gravel road, but the majority of mountain bikers prefer to ride trails they call singletrack. These are narrow trails that wind through forests or fields. Mountain bikers describe a sense of euphoria that results from singletrack or downhill riding.

For the most part, mountain biking can be split into four different categories:

• Cross Country is the most common form of mountain biking, and the standard for most riders. It generally means riding point-to-point or in a loop including climbs and descents on a variety of terrain.
• Freeride, as the name suggests is a 'do anything' discipline that encompasses everything from downhill racing (see below)without the clock to jumping, riding 'North Shore' style (elevated trails made of interconnecting bridges and logs), and generally riding trails and/or stunts that require more skill and "aggression" than XC. Freeride bikes are generally heavier and more amply suspended than their XC counterparts, but usually retain much of their climbing ability.
• Downhill is, in the most general sense, riding mountain bikes downhill. While cross country riding inevitably has a downhill component, Downhill (or DH for short) usually refers to racing-oriented downhill riding. Downhill-specific bikes are universally equipped with front and rear suspension, large brakes, and use heavier frame tubing than other mountain bikes. Downhill bikes are not meant to be pedaled up hill, therefore downhill riders and racers frequently employ trucks or ski lifts to be shuttled to the top of the hill. Downhill courses are the most physically demanding and dangerous venues for mountain biking.
• Trials riding consists of hopping and jumping bikes over obstacles. It can be performed either off-road or in an urban environment.