Flax is one of the oldest textile fibres. Evidence of its use has been found in the prehistoric lake dwellings of Switzerland. Fine linen fabrics, indicating a high degree of skill, have been discovered in ancient Egyptian tombs. Phoenician traders apparently brought linen from the Mediterranean area to Gaul and Britain, and the Romans introduced linen manufacture throughout their empire. In the 17th century the German states and Russia were major sources of raw material, and the linen industry was established in the United Provinces of the Netherlands, Ireland, England, and Scotland. In North America the expansion of the cotton industry reduced the importance of linen. Flax cultivation achieved importance in other areas, including Argentina and Japan, in the first half of the 20th century.

Flax is an herbaceous annual. When densely planted for fibre, plants average 0.9 to 1.2 metres (3 to 4 feet) in height, with slender stalks 2.5 to 4 millimetres (about 0.10 to 0.15 inch) in diameter and with branches concentrated at the top. Plants cultivated for seed are shorter and many-branched. The leaves, alternating on the stalk, are small and lance-shaped. The flowers, borne on stems growing from the branch tips, have five petals, usually blue in colour but sometimes white or pink. Small globular bolls, composed of five lobes, contain the seeds.

The plant, adaptable to a variety of soils and climates, grows best in well-drained, sandy loam and in temperate climates. In most areas planting of the same land with flax is limited to once in six years to avoid soil exhaustion. Cool, moist growing seasons produce the most desirable fibre. Harvesting usually takes place after the lower portion of the stalk has turned yellow but before the fruit is fully mature. The fibre is obtained by subjecting the stalks to a series of operations, including retting, drying, crushing, and beating.

Fibre colour ranges from buff to gray, with the best qualities creamy white. The fibre strands, which measure about 30 to 75 centimetres (12 to 30 inches) long, are made up of individual cylindrically shaped cells with fairly smooth surfaces.

Linen is valued for its strength, lustre, durability, and moisture absorbency. It is resistant to attack by microorganisms, and its smooth surface repels soil. It is stronger than cotton, dries more quickly, and is more slowly affected by exposure to sunlight. It can be bleached to a pure white but dyeing is somewhat difficult because the fibres are not readily penetrated. Although linen increases in strength when wet, the excessive use of alkalies in laundering can weaken the fibres. Low elasticity, imparting hard, smooth texture, also makes linen subject to wrinkling, which can be reduced by chemical treatment. Because linen absorbs and releases moisture quickly and is a good conductor of heat, linen garments have a cooling effect on the wearer.

Fine grades of linen are made into woven fabrics and laces for apparel and household furnishings. Lower grades are used for products requiring strength and ability to withstand moisture—such as canvas, twine, fire hose, bagging, industrial sewing thread, and fishnet. Leading producers include the Soviet Union, Poland, and Romania.