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Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species are assignable to families, it may not be noticeable that there is more than one code, but beyond this basic level these are rather different in the way they work.
The successful introduction of two-part names for species by Linnaeus was the start for an ever-expanding system of nomenclature. With all naturalists worldwide adopting this approach to thinking up names there arose several schools of thought about the details. It became ever more apparent that a detailed body of rules was necessary to govern scientific names. From the mid-nineteenth century onwards there were several initiatives to arrive at worldwide-accepted sets of rules. In the course of time these became the present nomenclature codes governing the naming of:
- Algae, Fungi and Plants – International Code of Nomenclature for algae, fungi, and plants (ICN), which in July 2011 replaced the International Code of Botanical Nomenclature (ICBN)
- Animals – International Code of Zoological Nomenclature (ICZN)
- Bacteria – International Code of Nomenclature of Bacteria (ICNB)
- Cultivated plants – International Code of Nomenclature for Cultivated Plants (ICNCP)
- Plant associations – International Code of Phytosociological Nomenclature
- Viruses – International Committee on Taxonomy of Viruses (ICTV); see also virus classification
Differences between codes 
Starting point 
The starting point, that is the time from which these codes are in effect (usually retroactively), varies from group to group, and sometimes from rank to rank. In botany and mycology the starting point is often 1753, in zoology 1758. On the other hand bacteriology started anew, making a clean sweep in 1980, although maintaining the original authors and dates of publication.
There are also differences in the way codes work. For example, the ICN (the code for algae, fungi and plants) forbids tautonyms, while the ICZN, (the animal code) allows them.
These codes differ in terminology, and there is a long-term project to "harmonize" this. For instance, the ICN uses "valid" in "valid publication of a name" (= the act of publishing a formal name), with "establishing a name" as the ICZN equivalent. The ICZN uses "valid" in "valid name" (= "correct name"), with "correct name" as the ICN equivalent. Harmonization is making very limited progress.
There are differences in respect of what kinds of types are used. The bacteriological code prefers living type cultures, but allows other kinds. There has been ongoing debate regarding which kind of type is more useful in a case like cyanobacteria.
Other codes 
A more radical approach was to replace all existing codes with a new BioCode, basically a synthesis of the existing Codes. The originally planned implementation date for the BioCode draft was January 1, 2000, but agreement was not reached.
A revised BioCode that, instead of replacing the existing codes, would provide a unified context for them, was proposed in 2011. The International Botanical Congress of 2011 declined to consider the BioCode proposal.
Another code in development is the PhyloCode, which would regulate phylogenetic nomenclature rather than Linnaean nomenclature (that is, it requires phylogenetic definitions for every name, and does not contain mandatory ranks). It will be implemented as soon as its companion volume will be published; that volume will contain phylogenetic definitions of some widely used names and serve as the starting point for priority.
See also 
- Ahoren Oren (2004). "A proposal for further integration of the cyanobacteria under the Bacteriological Code". Int. J. Syst. Evol. Microbiol. 54: 1895–1902. doi:10.1099/ijs.0.03008-0. PMID 15388760.
- "Draft BioCode". 1997.
- John McNeill (1996-11-04). "The BioCode: Integrated biological Nomenclature for the 21st Century?". Proceedings of a Mini-Symposium on Biological Nomenclature in the 21st Century.
- "The Draft BioCode (2011)". International Committee on Bionomenclature (ICB).
-  Greuter, W.; Garrity, G.; Hawksworth, D.L.; Jahn, R.; Kirk, P.M.; Knapp, S.; McNeill, J.; Michel, E.; Patterson, D.J.; Pyle, R.; Tindall, B.J. (2011). Draft BioCode (2011): Principles and rules regulating the naming of organisms. Taxon. 60: 201-212.
-  and  Hawksworth, D.L. (2011). Introducing the Draft BioCode (2011). Taxon. 60(1): 199–200.