One of the three large groups of organisms (apart from eukaryotes and bacteria), which have formed in the course of evolution.

Archaeae are microorganisms with similar features as the bacteria (simple cells without cell nucleus or organelles). Both groups have been termed prokaryotes. The genes responsible for central functions (like protein biosynthesis), however, are much more in accordance to those form eukaryotes than from bacteria. According to a new theory, archaeae were early precursors of eukaryotes.

Many archaeae are populating extreme habitats, which are only accessible to them. They are living for example close to hot marine springs (black smokers) or in drying salt lakes.