Bitter orange, Seville orange, sour orange, bigarade orange, or marmalade orange refers to a citrus treeand its fruit. It is native to southeast Asia, and has been spread by humans to many parts of the world. Many varieties of bitter orange are used for their essential oil, and are found in perfume, used as a flavoring or as a solvent. The Seville orange variety is used in the production of marmalade.

Bitter orange is also employed in herbal medicine as a stimulant and appetite suppressant, due to its active ingredient, synephrine. Bitter orange supplements have been linked to a number of serious side effects and deaths, and consumer groups advocate that people avoid using the fruit medically.

It is still not concluded if bitter orange affects medical conditions of heart and cardiovascular organs, by itself or in formulae with other substances.[10] Standard reference materials are released concerning the properties in bitter orange by the National Institute of Standards and Technology (NIST), for ground fruit, extract and solid oral dosage form, along with those packaged together into one item.

In the Americas, the juice from the ripe fruit is used as a marinade for meat in Nicaraguan, Cuban, Dominican and Haitian cooking, as it is in Peruvian ceviche. In Yucat√°n (Mexico), it is a main ingredient of the cochinita pibil.