Tansy (Tanacetum vulgare) is a perennial flowering herb in the daisy family (Asteraceae) native to Europe and temperate Asia. It grows upright with deeply divided aromatic leaves and flat clusters of bright yellow button-like flowers. The leaves and flowering tops were the parts most often used in traditional preparations.

In older herbal traditions, tansy was used in bitter formulas, washes, and household applications. Because the plant contains thujone and other potent compounds, modern herbal use is approached with considerable caution and the herb is better known today for its historical interest than for routine internal use.