Since the development of the sport in the 1970s many new subtypes of mountain biking have developed, such as cross-country (XC) biking, all-day endurance biking, Freeride-biking, downhill mountain biking, and a variety of track and slalom competitions. Each of these place different demands on the bike requiring different designs for optimal performance. MTB development has included an increase in gearing, up to 30 speeds, to facilitate both climbing and rapid descents. Other developments include disc instead of cantilever or V-brakes.

The history of the mountain bike includes contributions from cyclo-cross in Europe and the Roughstuff Fellowship in the UK. The name "mountain bike" first appeared in print in 1966 as "mountain bicycle". The mountain bike was a modified heavy cruiser bicycle used for freewheeling down mountain trails. The sport became popular in the 1970's in Marin county, California, USA. The 2007 documentary film, Klunkerz: A Film About Mountain Bikes, looks at this period of off-road cycling in detail. However, it was not until the late 1970s and early 1980s that road bicycle companies started to manufacture mountain bicycles using high-tech lightweight materials, such as M4 aluminium, although in recent years, titanium frames have become more common but can be very expensive. . The first mass production mountain bike was the Specialized Stumpjumper produced in 1982. Throughout the 1990s and 2000s, mountain biking moved from a little-known sport to a mainstream activity.

Mountain bikes can be classified into four categories based on suspension:

There are several different styles of mountain biking, usually defined by the terrain, and therefore bikes employed. Styles of mountain bike riding and mountain bikes have evolved rapidly in recent years leading to terms such as Freeride and "Trail bike" being used to categorise mountain bikes. Definitions for the most widely used terms are listed below.

Cross country (XC) mountain bikes are designed primarily around the discipline of cross country racing. Cross country racing with its emphasis on climbing as well as speed and endurance demands bikes that are both lightweight and efficient. In the 1980's and early 1990's XC mountain bikes typically consisted of a lightweight steel hardtail frame with rigid forks. Throughout the 90's XC bikes evolved to incorporate lightweight aluminium frames and short travel (65 to 110mm) front suspension forks. Recently full suspension designs have become more prevalent, the use of advanced carbon fibre composites has allowed bike designers to produce full suspension designs under 10kg. Full suspension bikes such as the Specialized Epic and the Merida Ninety Two have been successfully used to win the World Cross Country Championships. The geometry of Cross Country bikes favours climbing ability and fast responses over descending and stability and as a result typical head angles are 70-71o

Although intended for off-road use, Cross Country mountain bikes with their emphasis on lightweight construction are not designed for use on the most steep or severe terrain.

"Trail" Bikes are a development of XC bikes that are generally used by recreational mountain bikers either at purpose built "Trail centres" or on natural off-road trails. They usually have around 5" (120-140mm) of travel, weigh 11 to 15 kilograms (24 to 33 lb) , and have geometries slightly slacker than XC bikes, though not as slack as AM bikes. Examples include The Giant Trance, the Trek Fuel EX series, the Specialized Stumpjumper FSR, and others. With less of an emphasis on weight, Trail Bikes are typically built to handle rougher terrain than dedicated XC bikes while having slacker head angles (69-680) which provides greater stability while descending.

Enduro/all-mountain (AM) bikes bridge the gap between cross-country and freeride bikes, such as the Trek Remedy series, Specialized SX Trail, typically weighing between 13 to 16 kilograms (29 to 35 lb). These bikes tend to feature greater suspension travel, frequently as much as 6 inches (150 mm) or 7" of front and rear travel, often adjustable on newer mid- and high-end bikes. They are designed to be able to climb and descend well, these bikes are intended to be ridden on all-day rides involving steep climbs and steep descents, hence the term 'all-mountain'.

Freeride (FR) mountain bikes are similar to downhill bikes, but with less emphasis on weight and more on strength. Freeride bikes tend to have ample suspension and typically have at least 6 inches (150 mm) of travel. The components are built from stronger, consequently heavier, materials. They can be ridden uphill, but are inefficient and their moderately slack head tube angles make them difficult to maneuver while angled up a hill or traveling at a low speed. They are effective on technical downhill trails. Frame angles are typically steeper than those found in downhill bikes. This enhances maneuverability over and around small objects. Freeride bikes typically range in weight from 14 to 20 kilograms (31 to 44 lb). The most durable freeride bikes are often too heavy and have too much suspension to be ridden uphill as comfortably as other less-sturdy models, although newer, more expensive bikes come with suspension specifically designed to make them easier to ride uphill.

Downhill (DH) bikes typically have seven or more inches (178 mm) of suspension travel. They are built with frames that are strong, yet light, which often requires the use of more expensive alloys. In the past few years, lighter downhill bikes have been getting below the 40lbs mark (18 kg). Due to their typically large or high gears, long, plush travel and slack geometry angles, Downhill bikes are ideal only for riding down dedicated downhill trails and race courses. Downhill bikes have the most sag of Mountain Bikes to get ample traction to go fast over bumpy trails. Head Angles are often as slack as 64 degrees. Several types of bicycle speed records have been registered downhill.