International Patent Classification: Frequently Asked Questions

General questions

The acronym IPC stands for International Patent Classification.  It is a hierarchical classification system used primarily to classify and search patent documents (patent applications, specifications of granted patents, utility models, etc.) according to the technical fields they pertain.  It therefore serves as an instrument for an orderly arrangement of the patent documents, a basis for selective dissemination of information and a basis for investigating the state of the art in given fields of technology. 

The classification scheme contains about 70,000 entries identified by classification symbols that can be allotted to patent documents. These different classification places are arranged in a hierarchical, tree-like structure.

  • The highest hierarchical level are the eight sections of the IPC corresponding to very broad technical fields.  For example, Section C deals with "Chemistry and Metallurgy".
  • Sections are subdivided into classes (e.g. 120 in the eighth edition of the IPC.  Class C21, for example, deals with the "Metallurgy of iron").
  • Classes are further subdivided into more than 640 subclasses.  Subclass A21B, for example, deals with "Bakers' ovens; Machines or equipment for baking".
  • Subclasses are divided into main groups and subgroups.
  • Main group symbols always end with "/00".  For example, main group A21C 5/00 deals with "Dough-dividing machines".
  • The hierarchy of subgroups under main groups is designated by dots preceding the titles of the groups.

The IPC contains about 70,000 groups. Around 10% of the groups are main groups.

(see also paragraphs 6 and 7 of the Guide to the IPC)

You can find detailed information about the IPC on the WIPO IPC website.  This IPC homepage gives you access to the online publication of the IPC in English and French.

The site also provides links to documentation describing the IPC and its use (e.g. the official Guide to the IPC).  It also offers access to the documentation of the IPC revision process, i.e. documents and reports of different meetings of IPC bodies.

The IPC E-Forum serves as a place for exchanging information and documents related to the ongoing and completed projects of the IPC revision process.  It is freely accessible; however submission of documents and remarks is limited to participating patent offices.

Yes, you can initiate a search on the WIPO website and you can limit the scope of the search to the IPC area.

The Strasbourg Agreement is the legal foundation of the creation and revision of the IPC. On March 24, 1971, a Diplomatic Conference adopted the Strasbourg Agreement Concerning the International Patent Classification (IPC), which on that date was signed by 15 States.  Following that, the International (European) Classification of Patents for Inventions became de facto the 1st edition of the IPC.  The Strasbourg Agreement entered into force in 1975.  The members to the Strasbourg Agreement constitute the Special Union of the IPC.

The principal bodies of the IPC Union are the Assembly and the Committee of Experts. The IPC Committee of Experts has established a subsidiary body, the IPC Revision Working Group (IPC/WG).

The IPC/WG is in charge of the revision of the IPC and meets regularly twice a year in Geneva.  Participation is open to all members and observers of the IPC Union.

The administration of the IPC revision is carried out by the International Bureau of WIPO. 

The number of countries using the IPC when publishing their patent documents is much higher than the number of members of the Strasbourg Union;  the IPC is used in more than 100 countries in the world.  The IPC is so to speak the lingua franca of the patent classification. 

  • Use of the simplified IPC by industrial property offices PDF, Use of the simplified IPC by industrial property offices DOC, Use of the simplified IPC by industrial property offices

The authentic versions of the IPC are English and French.

Translations of the IPC are also prepared and published in other languages. For example, the IPC is available in the following languages through the "bridge" function of the Internet publication (click on the magnifying lens symbol  Links to other databases and classifications ):  Chinese, Czech, Dutch, Estonian, German, Japanese, Korean, Polish, Portuguese (Brazil), Serbian, Slovak, Spanish.

The IPC is used in more than 100 countries for classifying patent documents.  As such it is a very powerful tool for searching patent-related databases.  You can carry out a search (or you can modify your term based search) using IPC symbols in almost all patent-related databases.  Using the Cooperative Patent Classification (CPC), you can carry out a high precision search in the EP and US Patent documentation in their patent databases.  Using FI/F-terms, you can carry out a high precision search in the Japanese documentation.  However, the IPC is used universally all over the world which enables you to search, for example, both US and JP documents.

(see also paragraphs 19 to 23 of the Guide to the IPC)

The most comprehensive information about the structure, principles and rules of the IPC is collected in the Guide to the IPC.  The Guide is the official document approved by the bodies of the Strasbourg Agreement which explains the use of the IPC. It describes in simple terms and by means of examples the structure of the IPC and how the Classification should be used for classifying or retrieving patent documents.  The Guide is currently revised on a regular basis.

The Classification consists of several hierarchical levels:

A 01 B 33/00 Main group – 4th level
Section – 1st level     or  
  Class – 2nd level   33/08 Subgroup – lower level
    Subclass – 3rd level    

Subgroups may have different hierarchical levels;  their hierarchical level is indicated by their number of dots, with a lower level corresponding to a higher number of dots.

(see also paragraphs 19 to 28 of the Guide to the IPC)

(see also paragraph 41 of the Guide to the IPC)

In addition to hierarchical entries (sections, classes, subclasses and groups), the Classification contains also notes which are an integral part of the IPC.  Notes define specific terms, explain the scope of places and indicate how to classify.

A reference is a phrase followed by a symbol, between round brackets.  References indicate other places in the IPC where similar technology is classified.

References appear at the end of the titles of subclasses or groups.

(see also paragraph 38 to 40 and 48 of the Guide to the IPC)

The Official Catchword Index is an alphabetically ordered list of about 20,000 technical terms/keywords which refer the user to appropriate classification places. 

The German Patent and Trade Mark Office has prepared a more detailed version of a Catchword Index in German and English languages. It offers far more than 100,000 different entries. Catchwords can be used online as search terms in the IPC search function of the IPC website of the German Patent and Trade Mark Office.

The IPC is periodically revised for improving the system and for reflecting technical developments in its contents.  Between 1968 and 2006, the IPC was revised roughly every five years and, after each revision, a new edition was published.  The eighth edition of the IPC entered into force on January 1, 2006.  Since 2006, the IPC has been revised more frequently and each edition (called also version) is indicated by the year and month of its entry into force. Since 2010, the IPC is revised once a year and each new version enters into force on January 1.

(see also paragraphs 8 to 10bis and 42 of the Guide to the IPC)

The version indicator gives the edition/version where the corresponding entry was new or where its "file scope" was modified, for example, [4] or [2008.01].

(see also paragraph 42 of the Guide to the IPC)

From edition to edition, new entries appear in the IPC because there are new technologies for which the coverage was not sufficient in the previous edition.  Frequently, an existing "classification tree" was modified, because its original design did not fit the needs of the patent classifiers.  Often it was transferred to a new place where a new, different classification tree, was elaborated.

The consequence of this is that if you found an IPC symbol, you should check when it entered into the IPC. If it existed since the beginning, most probably you can initiate a reliable search with that.  However, if you have an edition indicator, e.g., [5], this means that the entry entered into the IPC in the 5th edition.  You have to check where technical subject of your interest was classified in the earlier editions.

To do this checking, use the Revision Concordance Lists.  If you used that symbol without any additional checking, you can automatically limit the scope of the search by limiting the time span covered only since the appearance of the 5th edition (1990).

With the reformed IPC, generally, there is no need to use previous editions of the IPC for searching because a major part of patent files is reclassified according to the revision changes.

For easier identification, new entries are presented in italics.


The Internet presentation of the current version of the IPC is available via the WIPO IPC homepage. In addition, many national intellectual property offices provide online presentations of the IPC.

Older versions of the IPC are also accessible via this online publication by selecting a version in the left-hand menu.

The IPC is also available in PDF format via the Internet publication at subclass level (see the corresponding  PDF  icon next to a subclass, e.g. A21D).


IPC-related files are available in DOC, HTML, PDF and XML formats on the IPC Download and IT Support Area. See also question "What IPC-related files does WIPO provide", below.

Search Terms: Having identified technical terms relating to the subject to be searched, the user should consult use the "Seach Terms" button in the IPC publication and insert these terms into the "Word(s)" field.  In order to allow wider search, the "Definition" and "Catchwords" boxes should be ticked.

Furthermore, the IPC publication provides electronic tools for determining possible classification entries:

  • IPCCAT: a linguistic tool that allows to enter short descriptions of technical subject matter, e.g. a summary or abstract, and retrieve suggestions where such subject matter could be classified. The tool is based on a neural network that was trained with a large set of patent documents that were classified by experts.
  • STATS: It is an assistant tools which provides IPC predictions based on statistical analysis of the patent documents (referenced in WIPO patent database PATENTSCOPE) containing the search terms specified by the user.

If the use of the Catchword Index or the other tools does not lead to a pertinent field of search, the user should scan the eight sections of the IPC, selecting possible classes by title.  Then it would be necessary to look at subclasses under the selected class and note a subclass which most satisfactorily covers the subject to be searched.  After selection of the appropriate subclass, the references and notes appearing in the subclass title should be checked for a more precise indication of the subclass contents.  Subclass definitions available in the electronic layer provide a more detailed description of the subject matter covered by a subclass than the rather concise title of a subclass.  These definitions should therefore be consulted if the user is not sure with respect to the scope of a subclass.

At the next step, all main groups in the subclass should be scanned for locating an appropriate main group. For a quick navigation in the subclass, a subclass index appearing at the beginning of the subclass could be used.  Again, the electronic layer also contains definitions for main groups.

Having determined the main group, the searcher should scan all one-dot groups under the main group and identify the group which seems most appropriate. In general, one-dot groups will have subordinate groups with two or more dots.  The group to be selected for search is the group which is most indented (i.e., has most dots) but which still covers the subject in question.

The above-mentioned definitions of subclasses and main groups also contain informative references to other places in the IPC which cover similar subject matter and could therefore be searched as well.

(see also paragraphs 135 to 155 of the Guide to the IPC)

There are two important classification systems used in addition by the largest patent offices (EP, US, JP), i.e. the EP and US joint CPC system and the Japanese FI system, both of the two systems are based on the IPC.

CPC is the Cooperative Patent Classification scheme used by the European Patent Office (EPO) and the United States Patent and Trademark Office (USPTO), which was jointly developed by the two Offices based in a large part on the existing European Classification System (ECLA) and on the USPC, respectively. It is based on the IPC, but it is much more detailed. CPC classification codes can be used to carry out searches on both the Espacenet and the USPTO Classification databases.

The more detailed subdivisions of CPC also serve as a source for the revision of the IPC.

FI or "File Index" is the internal classification system used by the Japan Patent Office (JPO) to classify their patent documentation and to organize prior art searches more efficiently. It is based on the IPC, but it is much more detailed.

Like CPC, the more detailed subdivisions of the FI classification scheme also serve as a source for revision of the IPC.

The electronic layer contains supplementary information which does not belong to the classification scheme of the IPC itself, for example, chemical illustrating formulae.  The electronic layer also includes other informative and illustrating material, such as classification definitions and illustrating drawings.  The electronic layer is accessible via the Inernet publication of the IPC (see the corresponding  Definition   or illustration  Illustrations   icons next to a subclass (e.g C07D) or a group symbol referring to definitions or illustrations).

(see also paragraphs 44 to 52 of the Guide to the IPC)

(see also paragraphs 44 to 47 of the Guide to the IPC )

The definitions are used for clarifying the exact boundaries of the subject matter appropriate for the classification place. They provide additional information in respect of classification entries and serve for their clarification, but do not change the scope of classification entries.

They consist of eight subsections:

  • "Definition statement"
  • "Relationship between large subject matter areas"
  • "References relevant to classification
  • "Informative references"
  • "Special rules of classification"
  • "Glossary of terms"
  • "Synonyms and keywords"

Definitions are provided only for a limited number of subclasses and groups. In the course of the further development of the IPC, definitions will be elaborated for all its subclasses, and for main groups and subgroups, where appropriate.  Definitions are accessible via the Internet publication of the IPC (a definition is available if there is a Definition shown next to a symbol.  See, for example, subclass G01S;  by clicking on the  Definition   will open the definition).

The Master Classification Database (MCD) is a database which collects regularly updated classification information for at least all patent documents belonging to the PCT Minimum Documentation PDF, PCT Minimum Documentation.  The rules governing the revision of the IPC require obligatory reclassification of all PCT Minimum patent documents which carry classification symbols affected by revision projects.  All such reclassification data is collected in the MCD and is from there available to the public via patent databases like PATENTSCOPE or Espacenet.

The standardized sequence is an alternative sequence of main groups in a subclass. While the ordinary sequence is based on the numerical order, i.e. group 2/00 comes after group 1/00 and 3/00 comes after 2/00, the standardized sequence defines an order where most specialized subject matter comes first.

The user of the IPC has the choice between the two representations only for the online publication.  The IPC in PDF format follows the numerical order of groups.

Technical questions

The complete IPC is available only via Internet; there is no printed publication of the IPC.  However, the Internet publication allows for print-outs of parts of the IPC, e.g. subclasses, through the hyperlink  PDF   next to the subclass title.  Please see also the printable PDF files in the IPC Download and IT Support area.

The IPC scheme is available for downloading in DOC, HTML, PDF and XML formats from the the IPC Download and IT Support area. All IPC-related files are available in XML format.  For a complete list of the files available refer to What IPC-related files does WIPO provide?.

For the current IPC, WIPO provides the following IPC-related files on the IPC Download and IT Support Area:

All  files are provided in  XML format.  WIPO's IPC homepage provides further documentation and DTD's of these files.

For more details, refer to document IPC master files specification DOC, IPC master files specification.

The validity file contains complete information on the validity periods of all classification symbols ever used in the IPC, i.e. it contains information on what date a particular symbol entered into force and on what date the valid use of this symbol ended.  If no such expiration date is given in the most recent validity file, the symbol is to be considered as valid for use.

The validity file does not contain any information on the titles associated with symbols.  However, it does give some more information for each symbol: it also indicates whether the symbol is to be used as indexing code or ordinary classification symbol.  For more details, see document "Specification of the validity file" available on the IPC Download and IT Support Area.

The Revision Concordance List shows in table form how technical subject matter was moved between subsequent editions.  It indicated from which deleted groups or groups with a changed scope of the previous edition subject matter was moved to groups of the new edition. It is generated based upon the "transferred to" and "covered by" notations in the IPC and it is completed with information coming from offices doing reclassification of their patent documentation.  You may view it via the internet presentation of the IPC (see the respective tab labelled RCL in the top-line) or download the XML version.

For more details, see document "Specification of the RCL DOC, Specification of the RCL.

No, you can download the IPC files, but you have to acknowledge WIPO's copyright if you plan to use the IPC on your site. 

Yes, please feel free to do that. URL parameters can be found in the Internet Publication (IPCPUB) URLs and Services specification.

Please inform WIPO if you established a link to our database to enable us to keep you informed if the IPC files are moved to new directories.

Standard ST.8: it specifies the machine-readable recording of classification data related to patent documents.

Standard ST.10/C: it specifies the presentation of bibliographic data on patent documents; classification information is part of the bibliographic data and related to the INID code 51.

Standard ST.36: It specifies details of using  XML for the exchange of information.

Further information relating to WIPO Standards.

ST.8 PDF is a standard dealing with recording of IPC symbols on machine-readable records. This standard has special importance in the international data exchange.

ST.8 prescribes that for each classification symbol allotted to a patent document a record in form of a fixed-length field with 50 positions should be provided.

New versions of the IPC enter into force on January 1 of every year.  Six month in advance, the new scheme, compilation and revision concordance files are available for downloading or consultation.