Linen ( /ˈlɪnɨn/) is a textile made from the fibers of the flax plant, Linum usitatissimum. Linen is labor-intensive to manufacture, but when it is made into garments, it is valued for its exceptional coolness and freshness in hot weather.

The word "linen" is cognate with the Latin for the flax plant, which is linum, and the earlier Greek linon. This word history has given rise to a number of other terms in English, the most notable of which is the English word line, derived from the use of a linen (flax) thread to determine a straight line.

Textiles in a linen-weave texture, even when made of cotton, hemp and other non-flax fibers are also loosely referred to as "linen". Such fabrics generally have their own specific names other than linen; for example, fine cotton yarn in a linen-style weave is called Madapolam.

The collective term "linens" is still often used generically to describe a class of woven and even knitted bed, bath, table and kitchen textiles. The name linens is retained because traditionally, linen was used for many of these items. In the past, the word "linens" was also used to mean lightweight undergarments such as shirts, chemises, waistshirts, lingerie (a word also cognate with linen), and detachable shirt collars and cuffs, which were historically made almost exclusively out of linen. The inside cloth layer of fine composite clothing fabrics (as for example jackets) was traditionally made of linen, and this is the origin of the word lining.^{[citation needed]}