In biology, a domain or empire is the top-level grouping of organisms in scientific classification. Originally three kingdoms were distinguished: the fauna for animals, the flora (Vegetabilia) for plants, and Mineralia (early authors also treated minerals in a third kingdom). This corresponds to the old saying animal, vegetable or mineral?.

Today there are several competing domain classifications of life.

• Three-domain system of Carl Woese, introduced in 1990, and featuring Archaea, Eubacteria, and Eukaryota.
• Two-empire system featuring Prokaryota (or Monera) and Eukaryota.

See also

• Kingdom (biology)