A beard is a growth of hair on the jaw and cheeks. All facial hair was once considered part of the beard. Hair grown on the upper lip is now called a moustache. The term "whiskers" commonly suggests the hairs of a long beard.

The appearance of facial hair is caused by the release of the testosterone hormone at puberty, and the rare case of female beard growth is an indication of hormone imbalance. The beard is usually wiry and often a different color from the terminal, or head, hair.

Throughout history the wearing or nonwearing of beards has been determined largely by religious customs or secular fashion and has often been considered a symbol of manhood and authority. Early Biblical, mythological, and historical figures, such as Adam, Abraham, Moses, Woden, King Arthur, and Charlemagne, are usually depicted with beards. In past ages, women with beards, like the three witches in Shakespeare's Macbeth, were thought to have supernatural powers.

The fashions of beards have varied considerably throughout history.

The ancient Egyptians shaved their faces for religious reasons. Although they were clean­-shaven, a false metal beard held in place by a chin-strap was a symbol of power and was worn by the Pharaohs and sometimes even their queens.

On the other hand, among the Jews, adult men were required to wear full beards, which they were forbidden to trim in the manner of neighboring tribes. To this day men of the ultraorthodox sect of Hasidic Jews wear long uncut beards.

The ancient Greeks wore beards. The great Homeric heroes were described as bearded, and Greek philosophers were distinguished by their long flowing beards. In Greek the word pogdno-trophos signifies a bearded man or a philosopher. Among the Greeks the custom of shaving is attributed to Alexander the Great, who insisted that all his soldiers should be clean-shaven, "to remove the handle that the enemy can seize", as he realized a long beard would give the enemy an advantage in close hand-to-hand fighting.

The early Romans wore their beards uncut until about 300 B.C., when barbers were introduced. The Roman general Scipio Africanus (237-183 BC) was noted as the first to shave regularly. In religious practice the Romans wore beards as a sign of mourning, whereas the Greeks shaved as a mark of respect. For a time Roman young men dedicated the cuttings from their first shaves to the goddess Fortuna, who in this connection was known as Fortuna Barbata. Gauls, who wore moustaches and no beards, were considered to be savages by the Romans.

Mohammed ordained the wearing of a beard to set his followers apart from shaven idolators, but they were required to clip their beards to distinguish themselves from the full-bearded Jews. In later times the Sikhs of the Punjab regarded the full beard, rolled up and pinned under the chin, as a mark of manliness.

The Anglo-Saxons wore beards prior to the seventh century AD, as did the Germanic tribes. Following the Norman Conquest of England, regular shaving was introduced, a custom among the clergy in northern France. Beards returned to popularity in the reign of Edward III of England (1312-1377), although in 1447 an English law was passed that forced men to shave their upper lip. Henry VII revived the beard, and in the sixteenth and seventeenth centuries European cardinals and priests wore beards. It was the fashion at the court of Elizabeth I to cultivate extravagant styles of beards.

Efforts to revive the custom of wearing beards during the reign of Henry I were vigorously suppressed by the clergy. Nevertheless, beards returned to popularity in the reign of Edward III (1312-1377) and were fashionable during the reigns of Francis I of France (1494-1547) and Henry VIII of England (1491-1547), who themselves wore full beards.

Beards were fashionable at the court of Elizabeth I (1533–1603) when many different styles were worn, among them the spade, the pique devant, the cathedral, the swallow-tail, and the bush. Many beards were colored golden as a compliment to the Queen, who had golden hair. Small, tufted beards were fashionable during the reign of Charles I (1625–1649). In the Victorian era beards were symbolic of wisdom and learning.

By the 18th century, beards had gone through successive periods of favor and disfavor. In 1705 Peter the Great of Russia made shaving compulsory and levied a tax on all beards and moustaches. Tax-collectors were stationed at the gates of each town and, when the tax was paid, the bearded recipient received a copper disk which showed he had paid his tax for the year.

No signer of the Declaration of Independence or of the Constitution wore a beard or even a moustache.

The return of the beard in the early 19th century was at first associated with revolutionary politics and Bohemian ways of life. Bearded men were stigmatized as radicals or social outcasts, and in the eastern United States beards were regarded unfavorably. By mid-century, however, whiskers had become a mark of Western pioneers and prospectors, and many well-known writers, scholars, and medical practitioners wore beards. Thus the beard gained respectability again. Significantly, Abraham Lincoln (1809–1865) was the first president to wear a beard.

During the American Civil War (1861–1865) beards were worn both by Union and by Confederate generals, many of whom had entered the war clean-shaven.

Until the early nineteenth century the guardsman's moustache was the hallmark of the French and Prussian military. In 1838 the king of Prussia issued an edict forbidding moustaches in his army. After 1840 the beard was regarded as being the mark of the French radical.

In the first half of the 20th century, beards went out of style in Western countries, particularly the United States. Ragged whiskers became a cartoonist's symbol for Bolsheviks and anarchists.

Certain famous men who still wore beards, Sigmund Freud and Bernard Shaw for example, stood out by contrast with the clean-shaven majority.

After 1945, beards became popular among artists, writers and rebels. The beatniks of the 1950s and the hippies of the 1960s wore beards to signify their social and political rebellion. This attitude has become progressively less common and beards and moustaches are now worn by many people of different age groups and social classes.