"Like all language, zoological nomenclature reflects the history of those who have produced it, and is the result of varying and conflicting practices. Some of our nomenclatural usage has been the result of ignorance, of vanity, obstinate insistence on following individual predilections, much, like that of language in general, of national customs, prides, and prejudices.

Ordinary languages grow spontaneously in innumerable directions; but biological nomenclature has to be an exact tool that will convey a precise meaning for persons in all generations".

J. Chester Bradley. Preface to the 1st edition of the International Code of Zoological Nomenclature, 1961.

The 4th edition of the International Code of Zoological Nomenclature, like the preceding editions and before them the R�gles internationales de la Nomenclature zoologique, has one fundamental aim, which is to provide the maximum universality and continuity in the scientific names of animals compatible with the freedom of scientists to classify animals according to taxonomic judgments.

The Code consists of Articles (which are mandatory) and Recommendations. The Articles are designed to enable zoologists to arrive at names for taxa that are correct under particular taxonomic circumstances. The use of the Code enables a zoologist to determine the valid name for a taxon to which an animal belongs at any rank in the hierarchy species, genus, and family (including subspecies, subgenus, and ranks of the family group such as subfamily and tribe). The Code does not fully regulate the names of taxa above the family group and provides no rules for use below the rank of subspecies.


There are certain underlying principles upon which the Code is based. These are as follows:

(1) The Code refrains from infringing upon taxonomic judgment, which must not be made subject to regulation or restraint.

(2) Nomenclature does not determine the inclusiveness or exclusiveness of any taxon, nor the rank to be accorded to any assemblage of animals, but, rather, provides the name that is to be used for a taxon whatever taxonomic limits and rank are given to it.

(3) The device of name-bearing types allows names to be applied to taxa without infringing upon taxonomic judgment. Every name within the scope of the Code (except for the names of "collective groups" and of taxa above the family group) is permanently attached to a name-bearing type. For species and subspecies this name-bearing type is either a single specimen or a number of specimens that together constitute the name-bearer; for genera and subgenera it is a nominal species; for taxa at ranks of the family group it is a nominal genus. Accordingly, when a taxon at any rank is delineated by a taxonomist it may contain several name-bearing types, each with a name that is available for use at that rank. The Principle of Priority (which may be modified in its operation in the interests of stability and universality - see (4) below) is used to determine which of those names is the valid one.

(4) Nomenclatural rules are tools that are designed to provide the maximum stability compatible with taxonomic freedom. Accordingly, the Code recognises that the rigid application of the Principle of Priority may, in certain cases, upset a long-accepted name in its accustomed meaning through the validation of a little-known, or even long-forgotten, name. Therefore the rules must enable the Principle of Priority to be set aside on occasions when its application would be destructive of stability or universality, or would cause confusion. For use in such cases the Code contains provisions that modify the automatic application of the Principle of Priority, whether it concerns the establishment or precedence of names, the fixation of name-bearing types, the spelling of a name, or any other matter.

(5) To avoid ambiguity, the use of the same name for different taxa must not occur and is prohibited. This is the Principle of Homonymy.

(6) The Code provides guidance for zoologists needing to establish new names, and rules to determine whether any name, previously proposed, is available and with what priority; whether the name requires amendment for its correct use, and to enable the name-bearing type of the taxon it denotes to be ascertained (and, when necessary, to be fixed).

(7) The Code also provides for its own interpretation and administration, by prescribing the constitution and operation of the International Commission on Zoological Nomenclature and the conditions under which the Code may be amended.

(8) There is no "case law" in zoological nomenclature. Problems in nomenclature are decided by applying the Code directly, and never by reference to precedent. If the Commission is called on to make a ruling on a particular case, the decision relates to that case alone.

Historical Background

The origin of an internationally accepted Code of Rules for Zoological Nomenclature is a consequence of the confusion of names that occured in the zoological literature of the early part of the 19th century. Following the publication of the 10th edition of the Systema Naturae by Linnaeus in 1758, and his adoption in it of binominal names for species of animals, the next century saw the new system expanded and developed in different places, and in different ways for different animal groups. By the second quarter of the 19th century disparate usages were common and the need for an agreement to achieve universality in the scientific names of animals and a greater stability had become apparent everywhere.

Moreover, the great explosion in known species, caused by the growth of science and by active exploration in countries outside Europe, resulted in a multiplicity of names; many of these were synonyms resulting from the work of scientists researching independently. It became critical to devise universally accepted methods for choosing between them.

The most important of the early attempts to regulate zoological nomenclature was that by Hugh Strickland. The rules proposed by Strickland and his colleagues developed into what has since been called the British Association Code or the Stricklandian Code; its official title was Series of Propositions for Rendering the Nomenclature of Zoology Uniform and Permanent. Following its presentation at the British Association for the Advancement of Science in 1842, by a Committee that included such distinguished zoologists as Charles Darwin, Richard Owen and John Westwood, that Code was translated and circulated widely and had great influence. It was published in France, Italy and the United States of America. It was received by the Scientific Congress at Padua in 1843, by the American Society of Geologists and Naturalists in 1845, and was adopted by the British Association for the Advancement of Science in 1846. It was revised in succeeding years, and provided the basis for the code formulated by Henri Douvill� (1881) which was adopted internationally by geologists, and for the American Ornithologists' Union Code (1886).

Following discussion at International Congresses of Geology (Paris, 1878; Bologna, 1881) it became clear that there was need for a formal international agreement to be made for rules to cover all zoological names, irrespective of which bodies or disciplines required to use them and applicable to both fossil and extant animals. At the 1st International Congress of Zoology (Paris, 1889), the Congress adopted, in part, rules drawn up by Maurice Chaper and Raphael Blanchard and referred the matter for discussion at the 2nd Congress (Moscow, 1892). The 3rd Congress (Leiden, 1895) appointed a Commission of five zoologists (R. Blanchard, J.V. Carus, F.A. Jentink, P.L. Sclater and C.W. Stiles) to formulate a "codex" and to report to the 4th Congress (Cambridge, England, 1898). This was the birth of the present International Commission on Zoological Nomenclature. Following the addition of ten more members and further consideration, a report was adopted by the 5th Congress (Berlin, 1901) and a Code of rules embodying the decision of that Congress was published in French, English and German in 1905. This Code, entitled R�gles internationales de la Nomenclature zoologique, with a series of amendments resulting from subsequent Congresses (Boston, 1907; Monaco, 1913; Budapest, 1927; Padua, 1930) remained in force until 1961 when it was replaced in its entirety by the first edition of the International Code of Zoological Nomenclature. This resulted from studies at Congresses following the 1939-45 War (Paris, 1948; Copenhagen, 1953; and London, 1958); a very detailed account of the work that culminated in the 1961 edition is given by Norman R. Stoll, Chairman of the Editorial Committee, in his Introduction to that edition. A second edition was published in 1964 incorporating amendments adopted at Washington (1963).

To most zoologists at the time, the 17th International Congress of Zoology (Monaco, 1972) appeared likely to be the last general Congress of Zoology. Decisions were taken there to amend the second (1964) edition, and in addition, to ensure mechanisms for continuity and future up-dating, a decision was taken to transfer responsibility for future Codes (and the Commission) from the International Zoological Congresses to the International Union of Biological Sciences (IUBS).

Responsibility for the Code and the Commission was accepted by IUBS at the XVIII IUBS General Assembly (Ustaoset, Norway, 1973). In response to proposals for major and substantive changes to the Code, made by the community of zoologists at that time, and to eliminate ambiguities, a third edition of the Code was prepared and was approved by the Commission, with the authority of IUBS, late in 1983 and published in 1985. An account of the changes adopted in that edition, comments on proposals, and the Commission's voting, are given in the Introduction to the edition.

A more detailed account of the development of zoological nomenclature and the events leading to the modern Code are given by Richard Melville, former Secretary of the Commission, in the centenary history of the Commission which was published in 1995 entitled Towards stability in the names of animals.

The decades of the 1970s and 1980s witnessed further marked changes in professional orientation and education of zoologists, changes in the methodology of taxonomy mostly resulting from new genetic information and the application of computers, a burgeoning literature, and accelerating changes in information technology including electronic publishing. It became clear that the Commission should work towards a fourth edition to accommodate the consequences of these and other factors, including a greater ecumenism in biological science leading to pressure within IUBS for greater consistency between the various codes of nomenclature.

An Editorial Committee was appointed by the Commission in Canberra in October 1988, and proposals were canvassed and discussed at meetings of the Commission and of the IUBS Section of Zoological Nomenclature in Maryland (1990) and Amsterdam (1991), and at meetings of the Committee in Leiden (1991) and Hamburg (1993). Following these, a Discussion Draft was publicly issued in May 1995. Within a year this resulted in almost 800 pages of comments from some 500 sources, many of which consisted of groups of zoologists; a number of these comments were published in the Bulletin of Zoological Nomenclature. All the comments (mostly transmitted by electronic mail) and the text were considered by the Editorial Committee in Vicenza in June 1996, and in August of that year a report was presented to the Commission and the Section of Zoological Nomenclature in Budapest. The comments showed that some of the tentative proposals in the Discussion Draft (such as a proposal for mandatory "registration" of new names and the abolition of gender agreement within combinations of generic and specific names) were not sufficiently acceptable to zoologists to be adopted. A revised draft was accepted by the Commission by postal vote (1997) with minor amendment. The Commission, in voting, made a number of suggestions for clarification which have been incorporated in this edition.

Concurrently with the work of the Editorial Committee of the present edition, and impacting on it, IUBS strongly supported studies and symposia to assess need for uniformity in biological nomenclature, and to examine difficulties that would have to be overcome before an acceptable code of biological nomenclature (a "Biocode") could be developed. The work has revealed that it would be premature to introduce into this edition major changes to the established principles and structure which underlie the Code. The separate codes have so diverged in fundamental ways since their earliest beginnings, that the introduction of common rules today, and their application to the names established under the separate codes and which are in stable use, would result in much nomenclatural instability. Presently, a greater degree of terminological uniformity is being striven for in all codes. But the lack of direct equivalence in meaning of such universally applicable concepts as "availability" (zoology) and "validly published" (botany and bacteriology - where the same term has different meanings) has made the task impossible for the present. However, despite this, work has advanced under the auspices of IUBS on developing a "Biocode" applicable for new names. Looking ahead to the future, if progress in all disciplines continues towards developing acceptable systems for registering new names, and officially listing all extant available names, so that rules protecting them can become a thing of the past, a single code will become a possibility.

The present edition

The modern International Code of Zoological Nomenclature is a complex and closely integrated document, no less so than its predecessors. In part its complexity results from its network of interdependent Articles. But the principal cause is the requirement that rules that are mandatory for current acts and new names must not upset actions taken by past generations operating under different, and less restrictive, nomenclatural rules or conventions.

For instance, many such names are products of the period before the R�gles when the application of the principle of name-bearing types, seen to be so fundamental today to the objective identification of names and for establishing synonymy, was not regulated. This principle was introduced into the rules for genus-group names with effect from 1931, and the obligation to explicitly fix name-bearing types for new species-group taxa is introduced only in the present edition. Prior to a strictly objective basis for identifying names to taxa, names could easily have been misapplied and very often they were. Therefore, as well as mandating for the precise identification of name-bearing types, the provisions relating to types must also provide for the protection of names which were established under less precise rules.

Because of the extent to which the provisions of the Code are interdependent, contradictory provisions and different wordings leading to conflicting interpretations can arise easily. Accordingly, its language must be precise; identical words and phrases must be used and re-used, and there must be extensive cross-referencing. To many zoologists, these requirements result in tedious and pedantic prose that will seem unduly legalistic to some. We make no apologies for the wording chosen, because we believe that interpretation must be beyond doubt even at the expense of elegance. Also to reduce ambiguity, the Glossary is an integral part of the Code: when a meaning is given in the Glossary, it is that meaning alone that must be used in interpretation.

Whether the Committee has succeeded in achieving the aim of providing a Code that can be interpreted easily by most practising taxonomists and others, only its application will tell. It is sobering to think that all who have drafted previous editions of the modern Code (and its predecessors) have hoped for the same.

Where experience has shown that some rearrangement of material from that in the previous editions would be desirable, we have done it. Otherwise, the fourth edition follows the arrangement of the third.

Development of underlying principles

The Code has always followed the underlying principle that, to be available, names must be published in multiple, identical, and durable copies. By this means it has effectively ensured that, irrespective of when and where they were published, names and the descriptions of new taxa would be permanently accessible and could be consulted most easily; moreover, there would be no doubt as to whether any name had been publicly presented in a form identical to all zoologists. However, it may be questioned whether the present policy effectively meets the aims of permanency and accessibility today, when electronic publication and communication is becoming an increasingly common medium of information exchange and search, and enormous quantities of ephemera meet the criteria of "publication".

During the last half-century the Code has gradually shifted away from the assumption, and later the requirement, that new names must be published by a method employing ink on paper. The R�gles of 1905 did not specify a particular method, but at that time most scientific information was distributed in works that were typeset and then printed with ink. Technology changed, and in 1948 the Paris Congress found it necessary to restrict publication to reproduction by ink on paper, a requirement that was incorporated in the 1961 edition of the Code. In the third edition (1985), the requirement for ink on paper was removed for new works with certain safeguards intended to eliminate most forms of ephemera. In the fourth edition read-only laser disks are admitted (subject to certain restrictions) as an acceptable method, but distribution by electronic signals is not. But it seems likely, in the longer term, and with the development of new information systems, that the solution will not lie in patching up a definition of publication but, rather, in scrapping it and finding a means of replacing "publication" as a primary determinant of availability.

A proposal to introduce registration of all new names as such a determinant was considered by the Commission in the development of the present edition. Public reaction was against it, a principal difficulty perceived by objectors being that no acceptable procedure is currently available; however, botanists seem likely to implement a system of registration for new names and it may be that their experience will, in time, produce a mechanism acceptable to solve the far greater difficulty (in terms of numbers of new names) in zoology. The most that the Commission has been able to achieve in this edition is to recommend to authors that all new names be brought to the attention of the Zoological Record and to require that every new name is explicitly identified as new in its original publication.

Progress is made in this edition to establish a mechanism to facilitate access to previously established names, and to achieve certainty that searches made for names are complete, by enabling international groups of specialists to compile lists of extant and known available names in major taxonomic fields, and to have these lists adopted by the Commission. Names not in a relevant adopted List would not be available. A similar policy has already been adopted for all genera and species in microbiology, where neither past nor new names are available unless they have been officially recorded.

Another major underlying policy issue currently being questioned is the adherence to Latin grammar which the Code requires in a number of its Articles; few zoologists today, or in the future, can be expected to have any understanding of that language and many find the requirements burdensome.

As in previous Codes, the present edition retains the requirement that Latin or latinized adjectival species-group names must always agree in gender with the generic name with which they are combined. A proposal was considered that would have allowed the names of species and subspecies to be treated as though they were arbitrary words (i.e. they were never to be treated as Latin adjectives), so that their spellings would be invariable irrespective of the gender of the generic name with which they are combined at any time. The proposal would not only have eased the burden on those without Latin, but would also have facilitated electronic searching. But, because the various ways proposed of achieving unchanging spellings were all considered to have drawbacks by the majority of respondents, and were not acceptable to them, the proposal was dropped. However, some changes are made in this edition to simplify the identification of gender in genus-group names, and the formation of stems for family-group names, and the Commission hopes these will reduce some of the difficulties of those without knowledge of Latin.

Perhaps the most significant operational change which the Commission has approved, is to introduce a number of automatic courses of action in cases which previously called for intervention by the Commission. These include requiring automatic departure from the Principle of Priority in certain cases in which the existing usage of names or spellings is threatened by the threatened revival of unused names proposed before 1900. Also when individual zoologists discover that the type species had been misidentified when a genus or subgenus was established, they are given the power to fix as the type species either the species actually nominated by the original author or the nominal species in conformity with the name in use. Cases in these two categories have been amongst the most common of those referred to the Commission, and the elimination of the need to refer them will prevent delay and uncertainty. Referral to the Commission remains the prescribed course in cases in which individual action by an author would be more likely to hinder than promote an acceptable outcome, and is always open as an avenue of appeal; it also remains open as a course of action for cases for which the Code does not provide an automatic solution.

The principal changes introduced in this edition are paraphrased below. The Code itself must be consulted for the wording of the actual provisions. The first three, concerning proposals of new names, confirm current professional practice.

Changes affecting proposals of new names

1. A new name published after 1999 is not made available unless it is explicitly indicated as being new (preferably by the use of a term such as "sp. nov.", "gen. nov.", "fam. nov.", "nom. nov.", or by a directly equivalent term in the language in which the paper is written).

2. After 1999 the proposal of a new species-group nominal taxon must include the fixation for it of a name-bearing type (a holotype or expressly indicated syntypes) in a manner that enables the subsequent recognition of that type.

3. When the name-bearing type of a species-group taxon proposed after 1999 consists of a preserved specimen or specimens, the proposer is required to include a statement naming the collection in which the name-bearing type is or will be deposited.

4. The proposal after 1999 of a new genus-group nominal taxon for trace fossils (an ichnotaxon) must include the designation of a type species.

5. An author establishing a new family-group name after 1999 may adopt a stem from the name of the type genus which is not properly derived from the genitive of the generic name according to the principles of Latin grammar, and the resulting spelling of the family-group name is to be maintained by subsequent authors (is recommended that, when necessary to avoid homonymous family-group names, authors take advantage of this provision and adopt the entire generic name as the stem).

Making lectotype designations

6. Lectotype designations made after 1999 are required to use the term "lectotype" or a direct translation of it, and be accompanied by a statement to the effect that the designation is made with the purpose of clarifying the application of the name to a taxon.

Matters affecting neotypes

7. If a previously lost holotype, syntype or lectotype of a species subsequently typified by a neotype is rediscovered, the original type specimen(s) will automatically displace the neotype and become the name-bearing type. If this causes confusion or instability an author should apply to the Commission for reinstatement of the neotype.

8. If the existing name-bearing type of a species-group taxon is indeterminate, so that the correct application of the name to a particular taxon is doubtful (i.e. the name is a nomen dubium), an author should request the Commission to set it aside and designate a neotype.

Changes affecting publication

9. A work not printed on paper issued after 1999 in numerous identical, durable and unalterable copies (e.g. on read-only laser disks) may be treated as published if the work itself contains a statement that copies in the form in which it was published have been deposited in at least five major publicly accessible libraries named in the work itself.

10. For purposes of zoological nomenclature, the following kinds of material are treated as unpublished:

(a) electronically distributed text or illustrations;

(b) down-loaded copies or printouts of such material;

(c) abstracts of papers, posters, lectures, etc., issued to participants at congresses, symposia and other meetings but not otherwise published;

(d) offprints (separates) distributed after 1999 in advance of the date of publication specified in the work of which the offprint forms part.

Measures empowering authors to act in the interests of preserving established usage

11. An author will be required (without a ruling by the Commission) not to displace a name which has been used as valid by at least 10 authors in 25 publications during the past 50 years, and encompassing a span of not less than ten years, by an earlier synonym or homonym which has not been used as valid since 1899.

12. In most cases an author will be required to maintain the particular spelling in prevailing usage for a name, even if it is found not to be the original spelling; for example, the spellings of family-group names currently in use are to be maintained even if formed from grammatically incorrect stems.

13. As already mentioned, if an author discovers that the type species fixation of a genus-group taxon was based on a misidentification of the type species, the author may, in the interests of stability and without making application to the Commission, fix as type species either the taxonomic species actually involved or the misidentified nominal species fixed previously.

14. If it is found that a name currently in general use for a family-group taxon is later than the name currently in use for one of its subordinate family-group taxa, the name used for the higher rank taxon is not to be displaced by the name of the subordinate taxon.

Lists of Available Names

15. The Commission is empowered, with safeguards, to adopt lists of names in major taxonomic fields. Names within the scope of such an adopted list but not listed in it will be treated as unavailable. Lists may only be adopted by the Commission which have been proposed by international bodies, and only after publication of the proposals, wide consultation with specialist committees and others, and taking into account public comment.


Taxonomists and other users of the Code will find in this edition, as in the previous ones, a compromise between adventure and conservatism that will not please everybody. Yet, in this compromise, the Code reflects the many contemporary voices of practising zoologists heard by the Commission in reaching its conclusions on proposals made by the Editorial Committee and published for comment in the 1995 Discussion Draft. Like its predecessors, the resulting Code is a mixture of clarifications of what was already in previous editions and new measures designed to meet the challenges of modern science.

The fourth edition will not be the last word. Zoologists generally, and the Commission in particular, will go on refining the wording of the Code to further reduce ambiguity and to make good deficiencies in its treatment of products of the past and present (and, as far as they can be foreseen, of the future). Both science itself and the social and technical systems within which scientists work are constantly changing, and the Code must continue to evolve to provide for these changes. Zoologists may remain confident that it will do so.

W. D. L. Ride
Chairman, Editorial Committee
The Australian National University,
Canberra, Australian Capital Territory.
May 1999