Aromatherapy is a form of alternative medicine that uses volatile liquid plant materials, known as essential oils (EOs), and other aromatic compounds from plants for the purpose of affecting a person's mood or health. Essential oils differ in chemical composition from other herbal products because the distillation process only recovers the lighter phytomolecules. For this reason essential oils are rich in monoterpenes and sesquiterpenes, as well as other VOC substances (esters, aromatic compounds, non-terpene hydrocarbons, some organic sulfides etc.).

Aromatherapy is a generic term that refers to any of the various traditions that make use of essential oils sometimes in combination with other alternative medical practices and spiritual beliefs. It has a particularly Western currency and persuasion. Medical treatment involving aromatic compounds may exist outside of the West, but may or may not be included in the term 'aromatherapy'