(species Secale cereale), cereal grass and its edible grain that is used to make rye bread and rye whiskey. The plant grows to a height of 1 to 2 m (4 to 6 feet) and has spikes composed of two or more spikelets bearing florets that develop one-seeded fruits, or grains. Rye cultivation probably originated in southwestern Asia about 6500 BC, migrating westward across the Balkan Peninsula and over Europe. Today rye is grown extensively in Europe, Asia, and North America. It is mainly cultivated where climate and soil are relatively unfavourable for other cereals and as a winter crop where temperatures are too cool for winter wheat. The plant, which thrives in high altitudes, has the greatest winter hardiness of all small grains, growing as far north as the Arctic Circle.

Rye is used chiefly as flour for bread, as livestock feed, and as a pasture plant. It is high in carbohydrates and provides small quantities of protein, potassium, and B vitamins. It is the only cereal other than wheat having the necessary qualities to make a loaf of bread, but it is inferior to wheat for the purpose, lacking elasticity, and is frequently blended with wheat flour. Because of its dark colour, a loaf made entirely from rye flour is called black bread. The lighter-coloured rye breads popular in Europe and the United States contain admixtures of wheat or other flours in addition to rye. Pumpernickel, a dark brown bread made wholly from unsifted rye flour, was a staple food in central and eastern Europe for centuries. Rye is also used in the production of rye whiskey. As livestock feed it is usually part of a mixture. The tough and fibrous straw of the rye plant is used less for feed than for litter or bedding, and it is also used for thatching, mattresses, hats, and paper. Rye may be grown as a green manure crop that is plowed under to improve the soil.

Russia and Ukraine together account for about a third of world production of rye. Other important rye-producing countries include Poland, Germany, Argentina, Turkey, and the United States.