recreation, sport, and mode of transportation that involves moving over snow by the use of a pair of long, flat runners called skis, attached or bound to shoes or boots. Competitive skiing is divided into Alpine (Alpine skiing), Nordic (Nordic skiing), and freestyle (freestyle skiing) events. Competitions are also held in events such as speed skiing and snowboarding.

Skiing also has long been employed for military purposes. Norwegian men on skis reconnoitred before the Battle of Oslo (1200). Ski troops were also used in Sweden in 1452, and from the 15th to the 17th century, skis were used in warfare (war) in Finland, Norway, Russia, Poland, and Sweden. Capt. Jens Emmahusen wrote the first skiing manual for Norwegians in 1733. Since 1767 there have been military ski competitions with monetary prizes. These competitions may have been the forerunner of biathlons (biathlon), which combine skiing and target shooting. Military skiing continued into the 20th century where snow conditions and terrain favoured their use for scouts and for a type of mounted infantry with a first-strike advantage against small objectives. In particular, ski troops fought in both World War I and World War II. Many veterans, especially of World War II, were very active in promoting the sport of skiing after returning to civilian life.

Skiing for sport in Europe, however, primarily developed after the publication of The First Crossing of Greenland (Paa ski over Grønland; 1890), Fridtjof Nansen's (Nansen, Fridtjof) account of his 1888–89 trans-Greenland expedition on skis.

At first Alpine skiers had to ascend on foot to a height before being able to ski down, which severely limited the number of downhill runs skiers could make in a day, even if they had the energy to keep climbing back up the slope. This changed with the introduction of a succession of devices in the 1930s—from rope tows to chairlifts and gondola lifts—that eliminated exhausting climbs up the slope and made it possible for one to ski downhill four to five times more in a day than earlier skiers could manage.

Nordic, or classic, skiing consists of techniques and events that evolved in the hilly terrain of Norway and the other Scandinavian countries. The modern Nordic events are the cross-country (cross-country skiing) races (including a relay race) and ski-jumping (ski jumping) events. The Nordic combined is a separate test consisting of a 15-km cross-country race and special ski-jumping contest, with the winner determined on the basis of points awarded for performance in both events.

The other important aspect of a cross-country race is the style of skiing. Until the 1970s there was only one style, now called classic, in which skiers follow parallel tracks. A more efficient type of cross-country skiing was popularized by American Bill Koch when he used a “skating” stride, pushing his skis outside the parallel tracks. This innovative style is now used in certain cross-country events. The skating technique requires longer poles and shorter skis than the classic style. It also requires higher boots that give improved ankle support.

Modern Alpine competitive skiing is divided into four races, slalom, giant slalom, supergiant slalom (super-G), and downhill (downhill skiing)—each of which is progressively faster and has fewer turns than its predecessor on the list. Super-G and downhill are known as speed events, which are contested in single runs down long, steep, fast courses featuring few and widely spaced turns. The slalom and giant slalom are known as technical events, which challenge the skier's ability to maneuver over courses marked by closely spaced gates through which both skis must pass; winners of these events are determined by the lowest combined time in two runs on two different courses. The Alpine combined event consists of a downhill and a slalom race, with the winner having the lowest combined time.

Alpine skiing made its Olympic debut at the 1936 Winter Games in Garmisch-Partenkirchen, Ger., where a combined race (featuring both downhill and slalom events) was held. The first giant slalom Olympic competition took place at the 1952 Winter Games in Oslo, and the supergiant slalom was added at the 1988 Winter Games in Calgary, Alta., Can. That same year the combined event, which had been removed from the roster of Olympic events in the 1940s, returned as an official event. It was dropped for the 1998 Winter Games in Nagano, Japan, however, in favour of two new events—the combined slalom (a slalom run coupled with a giant slalom run) and the combined downhill (comprising a supergiant slalom run and a downhill run). The 2002 Winter Games in Salt Lake City, Utah, once again featured an event that combined one downhill and two slalom runs. The 2006 Winter Games in Turin, Italy, included combined downhills and slaloms for men and women.

Freestyle skiing focuses on acrobatics and includes three events: acro, aerials, and moguls. Formerly known as ballet, acro was invented in the early 1930s in Europe. Utilizing moves from figure skating and gymnastics, the acro skier performs a 90-second routine set to music, in which jumps, flips, and spins are executed while skiing a 160-metre course on a gently sloping hill (12° to 15° incline). The performance is scored by judges on the basis of artistic impression and technical difficulty. The equipment for acro varies from that of Alpine skiing; the poles are longer and thicker, and the skis are shorter. In recent years, acro skiing has been losing out in popularity to the more gymnastic events.

Somersaulting and other tricks were exhibited before World War I, but it was not until about 1950 that such stunts (aerials) were popularized by Norwegian Stein Eriksen, who won a gold medal in the giant slalom at the 1952 Winter Games in Oslo. There are two varieties of aerials: upright and inverted. Flips or any movements where a competitor's feet are higher than his head are not allowed in upright competition. Instead, the skier performs such jumps as the daffy (with one ski extended forward, the other backward) or the spread eagle. In inverted competition contestants execute flips and somersaults, often reaching heights of some 50 feet (15 metres). The skiers build up speed on the inrun, which leads to various ramps and a landing hill with an incline of 34° to 39° and a length of about 100 feet (30 metres). On the basis of the degree of difficulty, the routine is scored on form and technique (50 percent), takeoff and height (20 percent), and landing (30 percent).

Mogul skiing, the navigation of large bumps (moguls) on the slope, was incorporated into competition shortly after introduction of aerials. Competing on a steep incline (22° to 32°) over a course of some 660 to 890 feet (about 200 to 270 metres), the mogul skier is scored on speed, turn techniques, and two mandatory upright jumps. There are also freestyle combined competitions in which skiers compete in acro, aerials, and moguls; the winner is determined by the total score of all three events.

Early skis designed for sport and recreation were made from one piece of wood, often hickory, but laminated constructions began to be used from the 1930s. In the 1950s plastic running surfaces on the bottom of skis increased their speed and durability. By the 1990s skis were typically made by surrounding a foam core with wood, wrapping both layers with fibreglass combined with Kevlar, aluminum, titanium, or carbon for strength, and finally adding a plastic base. As early as the 19th century, Norwegians and others had designed skis with sides that curved up to form parabolic profiles when seen from an end. Parabolic skis began to be widely used in the 1990s and are now standard for all Alpine skis. The unique shape of parabolic skis allows novices and intermediate skiers to master difficult turns more easily. Participation in recreational and competitive skiing continues to increase in popularity among people with disabilities, for whom specially modified equipment has been designed.

Typically the length of men's and women's Alpine skis should be close to the height of the skier, though somewhat longer skis can be handled by heavier or more experienced skiers. Alpine skis are generally about 3 inches (7.6 cm) wide. Cross-country skis are somewhat longer, narrower, and lighter than Alpine skis, and freestyle skis are somewhat shorter than Alpine skis. All types of skis—downhill (including slalom), jumping, cross-country (both for racing and touring), and freestyle—are pointed, turned up, and usually slightly wider at the tip (front) and shovel and squared at the tail (rear). They are thickest at the waist (midsection) under the foot and thinnest just before the ends. Skis are built with a camber, or a slight arch, so as to distribute the skier's weight along the length of the ski. Alpine skis once had a shallow groove running lengthwise along the centre of the bottom to give directional stability, but that feature is no longer necessary with parabolic skis. Alpine skis have sharp steel edges along the bottom to bite into hard snow or ice. Jumping skis are about 8.5 feet (2.6 metres) long and are wider, thicker, and heavier than downhill skis. They ordinarily have three grooves in the bottom and no steel edges.

Gösta Berg, Finds of Skis from Prehistoric Time in Swedish Bogs and Marshes (1950), is a foundational work on early skis. Olav Bø, Skiing Throughout History (1993; originally published in Norwegian, 1992), provides a general history of skiing, with an emphasis on Norwegian contributions. E. John B. Allen, The Culture and Sport of Skiing: From Antiquity to World War II (2007), shows the relationship between culture and skiing worldwide, and From Skiport to Skiing: One Hundred Years of an American Sport 1840–1940 (1993), covers the early history of skiing in the United States.