Rye (Secale cereale) is an important cereal crop in the cooler parts of northern and central Europe and Russia, cultivated up to the Arctic Circle and to 4000 m above sea level. The broad area of production includes Russia, Poland, Germany, Argentina, South Africa, Canada, and the United States. Rye is extremely hardy and can grow in sandy soils of low fertility. It is more tolerant of drought, cold, and other adverse growing conditions than are other cereal crops, is more winter hardy than all other small grains, and exhibits a greater amount of fall and early spring growth than do wheat (Triticum) or Oats (Avena sativa). Although spring and winter biotypes of Rye exist, most of the world supply is obtained from winter varieties. Cereal Rye is grown for grain, forage, hay, and as a weed-suppressing cover crop.

Because cereal rye matures earlier than other small grains, strict harvest and grazing management procedures are important to prevent it from becoming a weed. Feral rye is a serious problem in winter annual grain production in the western and central United States (feral plants are plants that are derived in part or fully from crop plants that have become partly or fully undomesticated, meaning they can reproduce on their own and are not dependent on managed cultivation). Feral rye is considered a weed of wheat and Barley (Hordeum vulgare) fields and was likely spread as a contaminant in the seed of domesticated cereals as they were introduced into new areas.

Rye was probably domesticated in eastern Turkey and Armenia, but more recently than wheat. In all Rye-producing countries more than 50% of the grain is used in animal feed, but it is also important in human nutrition. Rye is used in making "black bread", including pumpernickel, although the bread color may vary since the rye flour is often mixed with wheat flour, which lightens the color and adds gluten. Like wheat flour, rye flour can be used to make leavened bread, but the dough is less elastic and retains less carbon dioxide. Rye bread has a generally stronger flavor than wheat bread, has fewer calories, has a higher mineral and fiber content, and has a higher lysine content. A "sourdough process" involving lactic acid fermentation may be used in bread-making. (e.g., for "crisp bread"). Rye is used to make whiskey in the United States, gin in the Netherlands, and beer in Russia. Young plants are used as fodder for livestock. The mature straw is too tough for animal fodder, but can be used for bedding, thatching, paper making, and straw hats.

Ergot (Claviceps purpurea) is a fungus that parasitizes Rye and is poisonous to humans and livestock. Eating rye bread contaminated with Ergot may cause a range of disturbing symptoms.

(Vaughan and Geissler 1997; White et al. 2006)