In competitive rowing the oar is a shaft of wood with a rounded handle at one end and a shaped blade at the other. The shaft usually consists of two halves hollowed out and glued together in order to save weight and increase flexibility. The blade—a thin broadened surface—is either flat or slightly curved at the sides and tip to produce a firm grip of the water. The loom, or middle portion of the oar, rests either in a notch or oarlock (rowlock) or between thole pins on the gunwale (top edge) of the boat in order to serve as a fulcrum of the oar. The loom is protected against wear in this area of contact by a short sleeve of leather or plastic. Oars have fixed leather or adjustable metal or plastic collars, called buttons, to prevent slippage outboard. In sculling, the oars are called sculls.

Rowing began as a means of transportation. Galleys, used as war vessels and ships of state, prevailed in ancient Egypt (on the Nile River) and subsequently in the Roman Empire (on the Mediterranean) from at least the 25th century BC to the 4th century AD. Rowing was also an important adjunct to sailing for the Anglo-Saxons, Danes, and Norwegians in their waterborne military forays. Rowing in England, of both small boats and barges, began on the River Thames as early as the 13th century and resulted in a company of watermen who transported passengers up, down, and across the Thames in and near London. Wagering by passengers in different boats by the 16th century led to races, at first impromptu and later organized. By the early 18th century there were more than 40,000 liveried watermen. Doggett's Coat and Badge, an organized watermen's race, has been held annually since 1715. The watermen were, of course, professionals, and the regattas, programs of racing, held throughout the 18th century were also professional. A similar form of racing by ferrymen in the United States began early in the 19th century.

Local and national organizations, amateur and professional, were formed in this period, and in 1892 the Fédération Internationale des Sociétés d'Aviron (FISA; the International Rowing Federation) was founded. Events in rowing (for crews of eight, four, and two) and in sculling were established. In races for eights and for some fours and pairs, there is also a coxswain, who sits at the stern, steers, calls the stroke, and generally directs the strategy of the race. Rowing events in the Olympic Games have been held for men since 1900 and for women since 1976.

Events classified as lightweight are for women rowers not exceeding 59 kg (130 pounds) and men rowers not exceeding 72.5 kg (160 pounds). All rowers must weigh in between one and two hours before a race.

The racing stroke begins with the entry of the oar blade into the water (the catch). The stroke underwater follows, and then the travel of the blade out of the water (the recovery). Turning the blade horizontally by wrist motion as the oar handle is depressed to raise the blade clear of the water at the beginning of the recovery is called feathering. The extraction of the blade after driving the boat through the water is called the finish. Turning of the blade from horizontal to vertical in preparation for the catch is called squaring.

Early fixed-seat rowing used the English stroke: body swing produced most of the power, the arms being used mainly to transfer the weight of the body to the oar. With the introduction of the sliding seat (1857 in the United States; 1871 in England), leg drive was added. Later style changes introduced by Steve Fairbairn in 1881 emphasized leg drive and arm pull. The German coach Karl Adam in the 1950s produced good results when he introduced new training methods (Fartlek) based on Fahrtspiel (“speed play”), originally used for training runners, and on interval training (short sprints alternated with long runs).