α-Pinene is an organic compound of the terpene class. It is one of the two isomers of pinene, the other being β-pinene. An alkene, it contains a strained four-membered ring. It is found in the oils of many species of coniferous trees, notably Pinus and Picea species. It is also found in the essential oil of rosemary, Satureja myrtifolia, and many species of Seseli. Both enantiomers are known in nature; (1S,5S)- or (−)-α-pinene is more common in European pines, whereas the (1R,5R)- or (+)-α-isomer is more common in North America. The enantiomers' racemic mixture is present in some oils such as eucalyptus oil and orange peel oil.