In the taxonomy of microorganisms, the Euryarchaeota (Greek "broad old quality") are a phylum of the Archaea.

The Euryarchaeota include the methanogens, which produce methane and are often found in intestines, the halobacteria, which survive extreme concentrations of salt, and some extremely thermophilic aerobes and anaerobes. They are separated from the other archaeans based mainly on rRNA sequences.