International Code of Nomenclature of Prokaryotes (ICNP)


Changes Relative to the Current Edition of the Code

The ICNP is under active development and changes may be made to the current edition before they are incorporated into a new edition. The list of changes to the current edition approved by the ICSP can be found in the ICNP Editorial Board publications on the Journals and Publications page.


Current Edition of the Code

The current edition of the International Code of Nomenclature of Prokaryotes was revised in 2022 and published in a special issue of the IJSEM in May 2023. Compared to the 2008 revision, a large number of changes have been made following the compilation of all proposed changes to the ICNP by its Editorial Board and the subsequent vote on these proposals by the ICSP.

See: Oren A, Arahal DR, Göker M, Moore ERB, Rossello-Mora R, Sutcliffe IC. International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2022 Revision). Int J Syst Evol Microbiol 2023; 73:5585.

Previous Edition of the Code

The previous edition of the International Code of Nomenclature of Prokaryotes was revised in 2008 and published in a special issue of the IJSEM in January 2019. The draft of this document was presented at the Plenary Session of the Fourteenth International Congress of Bacteriology and Applied Microbiology (BAM), Montréal, 2014, together with updated lists of conserved and rejected bacterial names and of Opinions issued by the Judicial Commission. As in the past, it brings together those changes accepted, published and documented by the ICSP and the Judicial Commission since the last revision, published in 1990. Several new appendices have been added to this edition.

See:  Parker CT, Tindall BJ, Garrity GM. International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2008 Revision). Int J Syst Evol Microbiol 2019; 69:S1-S111.


Earlier Versions of the Code

Lapage SP, Sneath PHA, Lessel EF, Skerman VBD, Seeliger HPR, Clark WA. International Code of Nomenclature of Bacteria (1990 Revision). American Society for Microbiology, Washington, 1992.

The Editorial Board of the Judicial Commission of the International Committee on Nomenclature of Bacteria. International Code of Nomenclature of Bacteria. Int J Syst Bacteriol 1966; 16:459-490.

Buchanan RE, St John-Brooks R, Breed RS. International Bacteriological Code of Nomenclature. J Bacteriol 1948; 55:287-306.


Overview of the Code

The International Committee on Systematics of Prokaryotes (ICSP) and the International Code of Nomenclature of Bacteria are responsible for the naming of prokaryotes, including both eubacteria and archaebacteria or archaea. In the 19th century and the first half of the 20th century, bacteriologists tried to follow the provisions of the Botanical Code of Nomenclature, because bacteria had traditionally been considered fungi, the Schizomycetes. Methods of study were, however, very different. Also, much emphasis had to be put on cultural characteristics, so that type cultures were of critical importance. Type cultures are not permitted under the Botanical Code; therefore, at the First International Congress of Microbiology in Paris in 1930, proposals were made for bacteriology to establish its own Code of Nomenclature. A committee under the able guidance of the American bacteriologist R. E. Buchanan began work on this and, at the Second Congress in London in 1936, a draft Code was presented and placed under the aegis of the International Committee for Bacteriological Nomenclature [later, the International Committee on Systematic Bacteriology (ICSB), and now, the ICSP]. Buchanan condensed the provisions for nomenclature into a few broad principles that are still valid today:

  1. Names should be stable. This is assured by retaining the first name to be published, the principle of priority.
  2. Names should be unambiguous. This is assured by establishing type cultures, which can be referred to whenever there is doubt about the status of a novel bacterium. Type cultures are not necessarily completely typical, but they function as indispensable points of reference.
  3. Names should be necessary. This is assured by publication of descriptions of the organisms and the rejection of names that are superfluous.

Succeeding Congresses of Microbiology saw further drafting and included provision for a Judicial Commission to regulate Rules, and, where necessary, set them aside if they led to confusion. The first edition of the International Code of Nomenclature of Bacteria and Viruses was published in 1958. A journal for bacterial nomenclature was started, the International Bulletin of Bacterial Nomenclature and Taxonomy, later the International Journal of Systematic Bacteriology (IJSB) and now the International Journal of Systematic and Evolutionary Microbiology (IJSEM). The nomenclature of viruses was later transferred to the International Congress of Virology, and virus names are effectively decided by a committee set up for that purpose.

Between 1960 and 1980, considerable problems arose because a very large percentage of published names of bacteria could not be used, due to lack of good descriptions and type cultures. It became clear that the traditional starting date for plant names of Linnaeus in 1753 was unrealistic. Under the guidance of the Australian bacteriologist V. B. D. Skerman, a decision was made to make a completely new start for nomenclature of bacteria on 1 January 1980. Lists were made of names that could be satisfactorily associated with known bacteria, and these formed the foundation document, the Approved Lists of Bacterial Names, 1980. Names not on these lists lost standing in nomenclature (though provision was made to revive old names subject to certain safeguards). All new names had to be published in the IJSB (now the IJSEM) either by being described there, or, if described elsewhere, by placing them there in Validation Lists. All bacterial names are therefore found in a single journal, and it is not necessary to search the rest of the scientific literature for them. This has proved a great advantage for bacterial taxonomy.

At the same time, the Code was completely rewritten by the British bacteriologist S. P. Lapage to make it easier to follow and to put the Rules into a more logical order. Its main sections are Rules, which are obligatory, and Recommendations, which are guides to good practice. There are sections on how to describe, name and publish on a novel bacterium, and on how to request the Judicial Commission to look into nomenclatural problems. It also lists names that have been protected (conserved) and those that must be rejected, and advises on naming of infrasubspecific divisions. The statutes of the ICSB are included.

The most recent edition of the Code is the International Code of Nomenclature of Bacteria, 1990 Revision, published in 1992 by the American Society for Microbiology. A few amendments have been made since then, and these can be found in issues of the IJSEM. A number of moves have been made to unify the nomenclature of plants, animals and bacteria, and it is hoped that, in the future, there will be progress on these lines, especially to introduce registration of all names and avoidance of synonyms in different areas of biology. These aims will be greatly assisted by on-line databases of the scientific names of all organisms.

This overview was written by P. H. A. Sneath.