Hazel, or Hazelnut, a shrub or small tree of the birch family. Hazels grow in the temperate regions of Europe, Asia, and North America. There are about 15 species. Most hazels grow 8 to 30 feet (2.4 to 9 m) high. Their tooth-edged leaves are broad and heart-shaped. The tree has two sets of flowers—male and female—which grow in separate catkins (clusters). The male catkin bears yellow flowers; the female, yellow flowers with red tips. The fruit is a nut enclosed in a ragged-edged husk. The nuts are borne in clusters at the end of the branches.

Native American species include the common hazel and the beaked hazel, found in the eastern United States. The husk of the beaked hazel is bristly and extends beyond the nut to form a cylindrical beak. The California hazel grows on the west coast. The nuts of the American species are small, and the trees are not cultivated. The large hazelnuts of commerce, usually called filberts or cobnuts, are obtained from species native to the Eastern Hemisphere.

For centuries, hazel forks were used as divining rods in search for underground water. Hazel wood is used to make artists' charcoal. Hazelnut oil is used in the manufacture of perfumes.

The common hazel is Corylus americana; beaked, C. rostrata; California, C. californica. Hazel belongs to the birch family, Betulaceae.