Naming prokaryote taxa is an essential part in any description of new species, genera, families etc. There is no 'official', generally agreed, species concept for the prokaryotes, and there exists no official classification of Bacteria and Archaea. However, the nomenclature of the prokaryotes is governed by the general considerations, principles, rules and recommendations of the International Code of Nomenclature of Bacteria ('The Bacteriological Code'), a document approved by the International Committee on Systematic Bacteriology in 1990. A new version of the Code will soon be published, to be named the International Code of Nomenclature of Prokaryotes. After a short introduction explaining the provisions of the Code, this chapter provides a practical guide for the formation of names of new genera and species to comply with the rules of the Code and with the recommended orthography so that the newly formed names may be validly published. Examples are provided of correctly formed names added in recent years, and these examples should enable also those not versed in Latin and Greek to propose correct names to be attached to newly described species. Although stability of names is a major aim of prokaryote nomenclature, renaming existing species is sometimes necessary based on advanced insights into prokaryote systematics. Therefore, information is also given about the rules and current practice relating to renaming species. Special provisions exist for the nomenclature of the cyanobacteria, a group of prokaryotes traditionally covered by the rules of the International Code of Botanical Nomenclature.