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The hierarchy of biological classification's eight major taxonomic ranks. Life is divided into domains, which are subdivided into further groups. Intermediate minor rankings are not shown.

In biological taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest taxonomic rank of organisms, higher than a kingdom. According to the three-domain system of Carl Woese, introduced in 1990, the Tree of Life consists of three domains: Archaea, Bacteria and Eukarya. The arrangement of taxa reflects the fundamental differences in the genomes. There are some alternative classifications of life:

• The two-empire system or superdomain system, with top-level groupings of Prokaryota (or Monera), Eukaryota and the recently discovered Archaea empires.
• The six-kingdom system with top-level groupings of Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

As these groupings depend primarily on the analysis of genetic sequence data and cladistics, additional proposed arrangements are to be expected.

None of the three systems currently include non-cellular life.

See also

• Phylogenetics
• Systematics