Archaeas and Bacterias are both Prokaryotes. Both used to be classified in Monera kingdom, but later genetists found that they have actually very different genes, despite they both have a similar metabolism. So they think they have a totally different evolutionary origin and they decided to classify them in 2 different domains. The other domain, Eukarya, includes every other organism (all the ones who are not Prokaryots), which are: plants, animals, fungi and protists.
