IPC Classification System

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The International Patent Classification (IPC)

The International Patent Classification, or IPC, is administered by the World Intellectual Property Organization (WIPO). The scheme was conceived as an indexing system to organize patent documents from around the world based on the technical field of the invention, thereby providing a retrieval system by subject matter, independent of keyword searching.

The IPC can be searched for free at the official site.

The basic structure of an IPC mark is a hierarchy with 8 major sections (A-H). These are:

  • Section A – Human Necessities
  • Section B – Performing Operations; Transporting
  • Section C – Chemistry; Metallurgy
  • Section D – Textiles; Paper
  • Section E – Fixed Constructions
  • Section F – Mechanical Engineering; Lighting; Heating; Weapons; Blasting
  • Section G – Physics
  • Section H – Electricity

The structure of an IPC classification is made up of a Section, Class, Subclass, Main Group, and Sub-Group:










Main Group



Usually, the classifications are written with a space between the Subclass and Main Group, and a forward slash is included between the Main Group and Sub-Group, like so:

A61K 11/00

When searching, this conventional format may need to be modified in order to be consistent with the format accepted by a particular search engine. Some search engines even require the user to enter space-holder 0’s between the subclass and Main Group number. Most search engines provide this information in an easily accessible spot, such as a help guide.

Because the system is a hierarchal organization by technology, each progressive designation represents a more narrow band of subject matter within the higher definition. For example, take the classification above, A61K 31/01 (version 2001.01).


Human Necessities


Human Necessities: Medical or Veterinary Science; Hygiene


Human Necessities; Medical or Veterinary Science; Hygiene Preparations for Medical, Dental, or Toilet Purposes

A61K 31(/00)*

Human Necessities; Medical or Veterinary Science; Hygiene Preparations for Medical, Dental, or Toilet Purposes; Medical preparations containing organic active ingredients

A61K 31/01

Human Necessities; Medical or Veterinary Science; Hygiene Preparations for Medical, Dental, or Toilet Purposes; Medical preparations containing organic active ingredients; Hydrocarbons

*N.B. Main Groups are never written without a forward slash and corresponding subgroup; instead, primary main groups are always written with a /00 after them (where the subgroup is 00).

Major Recent Updates

February 2010

In February 2010, WIPO announced that work has begun to implement a simplified structure for the IPC which will enter into force with the new IPC edition released in January 2011[1] WIPO has made it known that the following "fundamental changes" will occur: [1]

  • The IPC structure will be simplified by abolishing the distinction between the core and advanced levels. Offices currently using the core level will be able to use the main groups in this unified structure. An updated IPC version will be published every year on January 1, with the possibility of a second publication in case of large numbers of modifications;
  • In view of the abolishment of the distinction between the core and advanced levels, the regular revision procedure of the IPC has already been simplified, and will be conducted by a unique technical body under the responsibility of the IPC Committee of Experts. New working procedures will enhance the use of the e-Forum, through which technical experts conduct consultations in pursuit of greater efficiency and quality of revision work;
  • Development of the IPC will be accelerated with the aim of building an integral, unified international patent classification by progressively integrating national or regional classification systems such as the United States Classification, the European Classification (ECLA) and the Japan Patent Office FI/F Term under the new working procedures;
  • A new electronic publication platform of the IPC has been developed, integrating the possibility of searching in the text of the IPC.

January 2010

The 2010.01 revision of the IPC served up the usual fare of class updates and changes. The following main classes were the also (heavily) modified according to Steve van Dulken:[2]

  • B62M, rider propulsion of wheeled vehicles
  • B65H, handling thin or filamentary material
  • C12N, micro-organisms or enzymes [especially stem cells in this revision]
  • F16H, gearing
  • G01Q, scanning probe techniques or apparatus [an entirely new class]

December 2008

On December 15, 2008 WIPO introduced revision to the IPC: IPC-9. Also known as IPC 2009.01, a guide to IPC 9 can be found here. A compilation of amendments can be found here.

The IPC-9 revision features several notable changes:

  • Clarification of Titles and other maintenance
  • Re-numbering of "...not provided for" subclasses to 99/00
  • Ceasing the production of hard copy versions of the core level booklets (now electronic only)

Major changes have been made to the following classes:

  • A01N65/00 Biocides
  • H04W Wireless Communication Networks
  • H04H Broadcast Communication

IPC Reform

Because IPC Reform is a complex subject, and some facets of it are both rather technical and not very useful to the average patent searcher, this section attempts to highlight the major features of the reform specifically as it affects patent searching endeavors.

The IPC system was introduced in 1968, and up until recently, was only revised about every five years. This slow revision schedule was a limitation, as the schedule was unable to react quickly enough to provide new classes for fast-emerging technology fields. As a response to this problem, the release of the eighth version, on January 1, 2006, marked the implementation of the reformed system. Under this system (called IPC-8, or IPC-R to designate “reform”) there is a double-designation for every patent document, consisting of Core and Advanced classification designations: originally, Core classifications were to be revised every three years from issue, while Advanced classifications were to be be revised every three months. The Core/Advanced designation is to be eliminated with the 2011 IPC reform, and a yearly revision schedule implemented.[1]

In addition to evolving quickly, the new system will stay current even on older publications. In the past, whenever a new IPC version was released, older documents were not re-classified based on the new system. For searchers, this meant that older classification definitions still applied to older documents, and a CD-ROM based concordance tool, called IPC:CLASS, was needed to effectively search in older art. However, as opposed to previous system revisions, the new version of the IPC has been retroactively applied to previous publications (at least those covered under the Minimum PCT Documentation.[3] Re-indexing previously published document collections, called the "backfile," was completed for major patent authorities before the IPC-R’s release*, and commercial databases now offer IPC-8 classifications extensively in their bibliographic data.

Although WIPO has implemented fast-evolving Advanced IPC categories to stay in synch with new technologies, its status as an international authority has required it to stay sensitive to the needs of small patent offices with limited examiner resources. The most important patenting authorities (i.e. patent offices that produce collections falling under the Minimum PCT documentation requirements) must assign classes using both the Advanced and Core IPC-R systems; in contrast, small and medium-sized patent offices may choose to only assign the broader, more stable Core classifications to their publications (since there are only about 20,000 Core classifications, as opposed to about 70,000 for the Advanced system, this reduces the classifying burden while increasing accuracy). Tiny, nascent organizations with limited resources can even use a simple Subclass-only designation as an IPC-R class on their publications.

One final need addressed by the IPC reform is the additional designation of IPC classifications based on inventive and non-inventive material disclosed in a patent document. In the past, classifications were assigned only for the inventive content of a document. However, examiners perceived that if a document could be indexed based on its non-inventive but still useful technical content, it would aid any examiners who might need to find that subject matter in a future search. Thus, non-invention classification codes can be added to a document on a discretionary basis to index it based on perceived useful content. But a mechanism was needed so that these discretionary codes would not artificially inflate IPC subgroups: The solution was to designate a separate "non-invention" classification for these documents. Because these codes are specifically designated as "non-invention," they can be systematically excluded from any IPC-R search by choosing to search in the "invention-only" fields.

Below is a review of each type of IPC-R classification: (Advanced and Core revisions will be eliminated with the 2011 revision of the IPC[1]):

  • Advanced (Designation to be eliminated with 2011 revision of the IPC[1]):
    • Revised every three months; associated "version" number equals the creation date.
    • Required use by all major patenting authorities (those covered under PCT minimum documentation requirements)
    • Can be more than one Advanced classification applied to a patent document

  • Core (Designation to be eliminated with 2011 revision of the IPC[1]):
    • Revised every three years; associated "version" number equals the creation date.
    • Designed for use by small-to-medium patenting authorities, without the resources to use the advanced system.
    • Similar to the advanced system, but with significantly fewer subgroups. Relies primarily (but not only) on main group levels (those with subgroup listed as /00).
    • Can be more than one Core classification applied to a patent document

  • Subclass Level:
    • Can be used by very small patenting authorities without the resources to designate Core classification levels.

In addition, there are two ways an IPC-R classification can be applied to a patent document: Invention and Non-Invention. In other words, while it is obligatory for examiners to assign at least one Advanced IPC classification code to a document to cover the inventive concept, examiners also have the option to assign discretionary codes to patent documents to indicate that subject matter contained within the document is representative of the state of the art, is non-trivial, or may be helpful to examiners in future searches.

WIPO defines invention information in the following excerpt from their Guidelines for Determining Subject Matter Appropriate for Obligatory and Non-Obligatory Classification[4]

"Invention information" in a patent document is all novel and unobvious subject matter in its total disclosure (e.g., description, drawings, claims) that represents an addition to the state of the art in the context of the state of the art (e.g. solution to a stated problem); "invention information" should usually be determined using the claims of the patent document as guidance.

"Addition to the state of the art" is the difference between the subject matter in question and the state of the art.

"The state of the art" is the collection of all technical "things" that have already been placed within public knowledge.

"Thing" means any technical subject matter, tangible or not, such as:

  • methods of using a product or performing a non-manufacturing operation;
  • products (articles of manufacture);
  • processes of making a product;
  • apparatus; and
  • materials from which a product is made.

"Inventive thing" means any part of the invention information which is novel and unobvious in itself.

WIPO states that all subject matter which qualifies as an addition to the state of the art must be classified under IPC-8. This type of classification is generally referred to as an "invention classification" and can sometimes be designated in search engines as "invention-only" (or similar).

Additionally, examiners have the option to classify further information at their discretion. This information could be "Any portion of the total disclosure of a patent document or of non patent literature (e.g., technical publication) that includes subject matter determined by a classifier or examiner to be useful for searching." This kind of classification is generally called a "non-invention class," and this (or a similar phrase) may be used to describe it by search providers.

Notes on the Backfile Reclassification Effort

The following are more in-depth details about how IPC-reform was carried out on a practical level for the millions of documents which were published prior to 2006.

Because of the huge number of patent documents that were already published under IPC-7, the reclassification efforts were restricted to one document per "simple" patent family (a restricted version of a patent family where the documents must share the same priority, divisionals, and continuations-in-part excepted). Thus, for documents published before 2006, the "classification picture" is stored on the family level and is identical for all members of that family, unless the publishing patent authority goes through a special procedure to reclassify any successive publications from that family.

The IPC-R reclassification effort was more of an automated process than a manual one. Most existing documents under PCT Minimum Documentation requirements were reclassified at the Advanced level by simply translating their already-present ECLA classifications into Advanced IPC-R using an EPO-produced concordance table. Similarly, Core-level classifications were then produced by using specially designed Advanced-to-Core concordance tables. The exceptions are the JPO, ROSPATENT, and EAPO–produced documents (Japanese, Russian, and Eurasian patent collections), which were never subject to ECLA classifications; thus, there was no way to translate ECLA classes into Advanced, and then Core, class designations for these documents. These individual authorities have assumed the burden of producing the re-classified data; as PCT minimum documentation countries, these collections must be classified at the Advanced level of IPC-R. Other patenting authorities may provide re-classified backfiles if they are interested, but are not required to do so.

Search Considerations

One major point that applies to all searching, including IPC classification searching: search with caution. The IPC reform effort has attempted to address complaints about the faults inherent in the old system, namely the inflexibility of the system to respond to new technologies or create divisions quickly enough when classes begin to get large. However, there is another major complaint about the IPC system, one that stems out of the requirement for every patent office around the globe to apply it: many examiners in national patent offices lack sufficient skill and training to appropriately apply the IPC classification system to their publications. This has caused an ongoing problem with the indexing quality that cannot be resolved by anything other than proper examiner training and quality review. To correct these errors, commercial patent indexing services such as Derwent World Patents Index and the Chemical Abstracts Service may sponsor initiatives to correct IPC indexing errors as they provide other value-added indexing services. However, full text commercial search providers do not systematically correct these errors by removing or adding new class designations. Therefore, class searching should always be performed in combination with other search strategies (like text-limited searching) to reduce the chance of overlooking misclassified documents.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 "Adoption of the simplification of the International Patent Classification System." WIPO website, http://www.wipo.int/classifications/ipc/en/news/2010/news_0007.html. Accessed on April 20, 2010.
  2. van Dulken, Steve. "Revision of the International Patent Classification." The Patent Search Blog website, http://britishlibrary.typepad.co.uk/patentsblog/2010/03/revision-of-the-international-patent-classification.html. March 24, 2010. Accessed on April 19, 2010.
  3. FAQ on IPC Reform. Hosted by the esp@cenet website, http://www.epo.org/patents/patent-information/ipc-reform/faq.html#16. Accessed July 17, 2007.
  4. "Guidelines for Determining Subject Matter Appropriate for Obligatory and Non-Obligatory Classification (i.e. "What" to Classify Within Patent Document Disclosures)." WIPO website, http://www.wipo.int/edocs/mdocs/classifications/en/ipc_ce_32/ipc_ce_32_12-annex6.doc. Accessed July 16, 2007.

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