Tansy is a perennial, herbaceous flowering plant in the genus Tanacetum in the aster family, native to temperate Europe and Asia. It has been introduced to other parts of the world, including North America, and in some areas has become invasive. It is also known as common tansy, bitter buttons, cow bitter, or golden buttons. The Latin word vulgare means "common".

Tanacetum is a genus of about 160 species of flowering plants in the aster family, Asteraceae, native to many regions of the Northern Hemisphere. They are known commonly as tansies. The name tansy can refer specifically to Tanacetum vulgare, which may be called the common tansy or garden tansy for clarity. The generic name Tanacetum means 'immortality' in Botanical Latin, since tansy was once placed between the burial sheets of the dead to repel vermin.