Circular RNA molecules were first described more than 40 years ago. However, it is only recently that the broadness of their phylogenetic distribution has been revealed. Since their discoveries, numerous studies have characterized the molecular mechanisms and function underlying these peculiar molecules, mostly in diverse eukaryotic species. In contrast, studies focusing on the biology of circular RNAs in archaea remain relatively scarce. In this chapter, we provide an overview of the discovery of circular RNAs in archaea and summarize our knowledge of their biology, with an emphasis on circular pre-ribosomal RNAs and Box C/D RNAs.