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905 Cooperative Patent Classification [R-07.2015]

Cooperative Patent Classification (CPC) is a bilateral classification system jointly developed by the United States Patent and Trademark Office (USPTO) and the European Patent Office (EPO). CPC is jointly managed and maintained by both offices and is available for public search for classification.

905.01 Classification Scheme for CPC [R-07.2015]

The CPC classification system arranges subject matter into hierarchical arrays.

  • (A) The highest array or level is the Section.
  • (B) Each section is subdivided into Classes.
  • (C) Each class is subdivided into one or more subclasses.
  • (D) Each subclass is broken down into Groups (main groups and subgroups).

Each part of this hierarchical structure is identified by classification symbols. Specifics about each element of the classification symbol are described below.

(A) Section Symbol – Each section is designated by one of the capital letters A through H and has an associated section title. There are nine sections, eight of which correlate to the sections of the International Patent Classification (IPC). The ninth section is used for classifying documents covering subject matter pertaining to a plurality of the sections. The table below shows the sections with their associated CPC and IPC section titles.

Letter Designation CPC Section IPC Section
A Human Necessities Human Necessities
B Performing Operations; Transporting Performing Operations; Transporting
C Chemistry; Metallurgy Chemistry; Metallurgy
D Textiles; Paper Textiles; Paper
E Fixed Construction Fixed Construction
F Mechanical Engineering; Lighting; Heating; Weapons; Blasting Engines or Pumps Mechanical Engineering; Lighting; Heating; Weapons; Blasting Engines or Pumps
G Physics Physics
H Electricity Electricity
Y General Tagging of New Technological Developments; General Tagging of Cross-over technologies spanning over several sections of the IPC; technical subjects covered by former USPC cross reference art collections and digest

(B) Class Symbol – Each class symbol consists of the section symbol followed by a 2 digit number (e.g., C07). Each class symbol is associated with a title.

(C) Subclass Symbol – Each subclass symbol consists of the class symbol followed by a letter (e.g., C07D). Each subclass symbol is associated with a title.

(D) Main Group Symbol – Each main group symbol consists of the subclass symbol followed by a one- to four- digit number, the oblique stroke, and the number 00 (e.g. C07D 203/00). Each main group number is associated with a main group title which precisely defines a field of subject matter within the scope of its subclass and a definition.

(E) Subgroup Symbol – Each subgroup symbol consists of the main group symbol, but the number "00" in the main group symbol is replaced with an alternative number of up to six digits (e.g. C07D 203/02). Each subgroup symbol is associated with a title and definition.


CPC Symbols C07D 203/00 or C07D 203/02

Example: CPC Symbols C07D 203/00 or C07D 203/02

905.01(a) CPC Titles [R-07.2015]

The title associated with a CPC symbol defines the scope of the subject matter covered by that symbol. In general, the title of every CPC organizational division is read as including the titles of all its superior organizational units. For example, the title of a CPC subgroup is interpreted as including the title of its parent group and that parent’s group title all the way up to, and including, the section title.

Titles in the CPC system are generally in the form of single part or multipart titles which are described below.

  • (A) Single part title -- Defines or represents the subject matter of a single concept or information.
  • Example:
  • A47C 1/00 Chairs adapted for special purposes
  • (B) Multipart title (separated by semicolons) -- A semicolon in a CPC title delineates coverage of two distinct and separate information entities that should be considered stand-alone things for purposes of coverage.
  • Example:
  • The three semicolons in the above example inform us that the subclass covers four distinct and separate entities: 1) refrigerators, 2) cold rooms, 3) ice boxes, and 4) other types of cooling or freezing apparatus not covered by any other subclass, therefore it is a residual to all cooling and freezing apparatus not elsewhere classified in CPC.

905.01(a)(1) References within CPC Titles [R-07.2015]

References are statements enclosed within parentheses in titles. The references point to other classification places that may be of interest. References apply to the classification place they appear and to all hierarchically lower classification places, unless stated otherwise.

Examples of References:

Examples of references enclosed within titles in parentheses


B64C AEROPLANES; HELICOPTERS (air-cushion vehicles B60V)

(A) Limiting references

A limiting reference is found in the group titles of the scheme and exclude specific subject matter from the scope of the classification place, when this subject matter would otherwise fulfill all the requirements of the classification place (or would be covered by that place). Limiting references are pertinent for classification purposes. Limiting references limit the scope of a place, thereby avoiding overlap.


A01F 7/02 . With rotating tools (threshing cylinders or concaves A01F 12/18)

(B) Precedence references

A precedence reference is a special example of a limiting reference that always refers to another group or groups taking "precedence" within the same subclass. The purpose of a precedence reference is to remove overlap between two similar groups.


G02B 1/00 Optic elements

1/04 . made of organic materials (1/08 takes precedence)

905.01(a)(2) Notes Found in CPC schemes [R-07.2015]

Notes are supplementary statements that follow a CPC class, subclass, main group, or subgroup title. Instruction in a "Note" is applied only to the CPC place where it appears, including all its hierarchically lower places. For example, a note after a class title applies to the entire class. A note after a subclass title applies only to the subclass, a note after a main group applies only to the main group, etc. Notes may be used to explain the scope, define terminology, or indicate specific classification rules.

905.01(a)(3) Warnings Found in CPC schemes [R-07.2015]

A warning is used in CPC schemes for signaling deviations from IPC or incomplete classification. A warning may include a listing of IPC groups not included within CPC and the CPC group which covers the relevant subject matter. A warning also may be used to indicate the deletion or transferring of CPC groups and reclassification notices.

905.01(a)(4) Guidance Headings Found in CPC Schemes [R-07.2015]

Guidance headings may be provided as follows:

  • (A) When a large part of a subclass relates to a common subject matter, a guidance heading indicating that subject matter may be provided at the beginning of that part.
  • (B) As a title, without any associated symbol, of subject matter preceding several main groups.
  • (C) To describe common subject matter of several main groups.

905.02 CPC Definitions [R-07.2015]

Each CPC definition, whether it is a subclass, main group, or subgroup definition, must adhere to the same definition template which defines the permissible elements and formatting. Most CPC schemes will include supplementary definitions to clarify the scope of classification places as well as to inform the user of special classification rules in that area. Definitions are provided for CPC subclasses, main groups or subgroups, but not for CPC sections or classes. Not all CPC subclasses or groups have definitions. When a title is sufficiently clear to describe the scope of the classification place, a definition statement is not necessary.

A definition may include the following:

  • (A) Definition title – The definition title always reflects the title of the classification place being defined. For example, a subclass definition will have the same title as the title of the subclass; a group definition will have the same title as the title of the group.
  • (B) Definition Statement - The scope of the definition statement should essentially be the same as the scope of the title. The definition statement should clearly elaborate the meaning of the classification place rather than merely restating its title. The definition statement should provide a positive description of the subject matter appropriate for the classification place, rather than a negative description of the subject matter excluded from the classification place. The appropriate classification places for the excluded subject matter are found under "Limiting References".
  • (C) References relevant to classification in a subclass/group
    • (2) Specially adapted references – Specially adapted references are references from function-oriented (general) to application-oriented places. The subject matter indicated by a specially adapted reference could be classified in the instant classification place, and in the classification place where the reference points to, or both.
    • (3) Residual references – Residual references from residual subclasses (defined as such in the title of the subclass or the definition statement) to non-residual places should appear in this section.
    • (4) Informative references -- Informative references are references that indicate the location of subject matter that could be of interest for searching, but are not within the scope of the classification place where the reference occurs. References from application-oriented places to function-oriented places are informative.
  • (D) Special rules of classification within the subclass/group -- This section contains special classification rules, which apply only within the subclass/group and not between subclasses/groups. Examples of such classification rules are the first place or the last place priority rules.
    • (1) First place priority rule: When a document is classifiable in more than one group in a scheme, the one highest in the scheme is allocated to the document.
    • (2) Last place priority rule: When a document is classifiable in more than one group in a scheme, the one lowest in the scheme is allocated to the document.
    • (3) Common rule: When a document is classifiable in more than one group in a scheme, the classification symbol that most completely covers the invention is allocated to the document.
    • In CPC, as with IPC, in the absence of any classification rule, common rule, defined in (D)(3) above, is the governing classification rule.
  • (E) Glossary of terms -- This section consists of definitions for significant words or phrases found in the titles or definition statements. Terms found exclusively in patent documents or in technical literature, but not in the scheme or the definition statement, will normally appear in the synonyms and keywords section.
  • (F) Synonyms and Keywords - This is an optional section establishing synonyms, keywords, abbreviations and acronyms from terms used in the patent documents themselves or in technical literature. This section aids in formulating search queries in electronic searching in the technical field. This section may include definitions of such terms when they do not appear in the scheme or the definition statement.

905.03 Classifying in CPC [R-10.2019]

The primary purpose of classification is to facilitate the retrieval of technical subject matter. In order to reliably retrieve technical subject matter using the CPC classification system it is important for all technical subject matter to be consistently classified.

CPC has its own classification rules which appear in the scheme, definitions, or both. See MPEP § 905.02. In the absence of any specified classification rules in the scheme and definitions, classification practice follows the rules used in the IPC, as set forth in the IPC Guide. The IPC Guide is available at

905.03(a) The CPC Database [R-07.2015]

The CPC database maintains technical information regarding the patent family documents for each patent document included. Patent documents contain two types of technical information to classify. These are invention information and additional information.


A patent family is a group of documents related to each other by common priorities. Examples include a pre-grant publication (PGPub) of an application and any patent issued from the same application. A parent and divisional application also are considered as being in the same family.

In the CPC database, CPC symbols are associated with patent families. When a document is classified in CPC, the symbol associated with the document is stored in the CPC database as an association between the symbol and patent family in which the document is a member. This means that whenever a CPC symbol is allocated to a document all the documents in the family receive the same symbol.

In the CPC database, a document cannot be classified independently of the other documents belonging to the same patent family. Every classification symbol associated with a document, i.e., allocated to the document, is associated with every patent document in the family. Each allocation of a symbol to a patent family has additional attributes stored in the CPC database. These include the following:

  • Classification symbol
  • Type (Invention/other additional information)
  • Position (First/later classification)

All disclosed invention information in a patent document must be classified in CPC in order for a user to retrieve the invention information from the system. Therefore, it is mandatory to classify all the invention information disclosed in each family to be classified.

Invention information is technical information in the total disclosure of a patent document (for example, description, drawings, claims) that represents an addition to the state of the art. The invention information is determined in the context of the state of the art, using guidance provided by the claims of the patent document, with due regard given to the description and the drawings. "Addition to the state of the art" means all novel and unobvious subject matter specifically disclosed in a patent document, which advances the state of the art, i.e., the technical subject matter disclosed that is not already in the public domain.

Patent documents should not be classified as a single entity. Rather, all different inventive entities, claimed or disclosed within the patent document, should be identified and separately classified. Such different inventive entities are represented by different claims, alternative variants or different categories of subject matter (for example, a product and a method of its production).


Additional information is non-trivial technical information which does not in itself represent an addition to the state of the art but might constitute useful information for the searcher. The additional information complements the invention information by identifying the constituents of a composition or mixture; elements or components of a process or structure; or use or applications of classified technical subjects.

Unlike invention information which must be classified, any additional non-trivial technical information that would be useful for search is classified on a discretionary basis.

A.Type Attributes

Every classification allocation has a "type" attribute. There are two values that this attribute may have:

  • (A) Invention Information
  • When allocating CPC symbols to a document based on disclosed invention information, the type attribute is set to "invention." This is typically done by putting the symbol being allocated in the "mandatory" section of the classification form.
  • (B) Additional information
  • When allocating CPC symbols to a document based on disclosed information that is not inventive, the type attribute is set to "additional". This is typically done by putting the symbol being allocated in the "discretionary" section of the classification form.
  • (C) Position Attribute
    • First - Each patent family will possess a first-listed CPC classification symbol which is selected from the required classifications for the inventive subject matter of the patent family. This "first" CPC classification is the inventive classification symbol which most adequately represents the invention as a whole for the patent family. In situations where a later-published family member possesses a different first-listed CPC classification, this will override the previous first-listed classification (which will be retained for the patent family as an inventive classification symbol). There is one and only one "first" position attribute per patent family. The first attribute is associated with the invention symbol that most completely covers the technical subject matter of the disclosed invention. The first position symbol is identified as the first mandatory symbol listed on the classification form.
    • Later - If a symbol allocation is not the "first" position symbol, its position attribute is "later". All invention allocations that are not "first" position, as well as all "additional" type symbols have the position attribute "later". All symbols listed on the classification form other than the first listed invention symbol receive the position attribute "later" .

905.03(b) Approach to classification in CPC [R-07.2015]

The first step to classifying a document in CPC is to identify the subject matter that will be classified. The second step is to identify appropriate groups in CPC covering the subject matter to be classified.

The general rules for identifying the subject matter to classify in CPC are as follows:

  • (A) All subject matter covered by the claims of a patent document must be classified as invention information along with any novel and unobvious constituents or components (subcombinations) of the claimed subject matter. Classification should be based on the subject matter of each claim as a whole and on each inventive embodiment within a claim.
  • (B) Any unclaimed subject matter in the disclosure that is novel and unobvious must also be classified as invention information.
  • (C) It is desirable to classify or index any additional information complementing the invention information, mentioned in the claims or in the unclaimed disclosure, if it is useful for search purposes.
  • (D) A subcombination of the subject of the invention if the subcombination is itself novel and non-obvious.

The scheme or definitions in particular areas should be consulted to determine if additional classification or index codes are required. For example, places in CPC where multi-aspect classification is especially desirable are indicated by a note. See MPEP § 905.02. Depending on the nature of the subject matter concerned, such a note prescribes obligatory classification of the subject matter according to the indicated aspects, or contains a recommendation for multi-aspect classification if it is desirable for increasing the efficiency of the patent search.

The general procedure for identifying the appropriate groups for covering the subject matter to be classified is as follows:

  • (A) Identify the appropriate subclasses covering the subject matter to be classified.
    • (1) The scope of a subclass is defined by its title and definition. In order to determine a candidate subclass for classification one must review the titles of available subclasses for scope coverage.
    • (2) After a candidate subclass has been identified, the subclass notes, references and definition should be consulted to verify that the scope of the subclass covers the subject matter to be classified.
    • (3) The preceding steps should be repeated until a candidate subclass is verified to cover the subject matter to be classified.
  • (B) Identify the appropriate group(s) covering the subject matter to be classified.
    • (1) Identify candidate main groups that cover the subject matter to be classified.
    • (2) Verify that the notes, references, and definitions do not exclude the subject matter to be classified, and that the group is in active use (not under reclassification).

    The technical subject matter of many inventions is completely covered by only one group in the subclass. In this situation, classification is made in the one group covering the technical subject matter of the invention.

    When multiple groups cover the technical subject matter of a single invention, classification is generally made in the group which most completely covers the invention. Within a group array, a group that covers the technical subject matter of the invention to be classified generally covers the subject matter more completely than the parent of that group.

    When multiple groups cover the invention equally well, groups are selected according to the following rules:

    • (a) In the case where the Last Place Priority Rule (LPPR) is applicable to the groups under consideration, then the group lowest in the scheme is selected for classification.
    • (b) In the case where the First Place Priority Rule (FPPR) is applicable to the groups under consideration, then the group highest in the scheme is selected for classification.
    • (c) In the case where neither LPPR nor FPPR are applicable to the groups under consideration, then classification is made in each group.
    • (3) Whenever classifying into a group, the scheme notes and definitions should be consulted for guidance regarding special rules of classification applicable to the CPC groups at issue, such as the requirement for Multiple Aspect classification or Indexing.
    • (4) Whenever classifying into a group, the scheme should always be consulted for precedence notes and references that indicate a preference for classification in another group. Precedence notes and limiting reference should always be followed when applicable.
    • (5) Identify application/functional classification places. Occasionally, two or more subclasses/groups are identified that cover the disclosed invention information from different aspects. For example, one classification place might cover specific uses of the invention, whereas the second classification place may cover the generic uses of the invention. These types of coverage are respectively referred to as application and functional classification places. In general, classification is made in the application classification place when application specific adaptations are disclosed. For example, a pump specially adapted to replace a heart is classified in A61M 1/10, whereas pumps, in general, without any disclosed special adaptation are classified in F04B, F04C, F04D, or F04F depending on the specific structure of the pump. When uses of inventions are nominally disclosed, classification is generally made in functional classification places.
    • (6) Identify genus/species classification places.
      • (a) In the case where an invention is generically disclosed classification is made to the classification place covering the generic invention. Even in cases where species are nominally disclosed, such as by name only, classification is still made to the generic classification place.
      • (b) In the case where fully enabled species are disclosed, classification is required in the classification places covering the individual species.
    • (7) Identify residual classification places

      In the event a classification place that explicitly covers the technical features of the invention to be classified cannot be identified, then classification should be made to a "residual" classification place. Residual classification places can be found at both subclass and group levels. Residual classification places are identifiable by their titles, which typically indicate they cover subject matter not elsewhere covered.

905.03(c) Combination Sets [R-07.2015]

In certain CPC fields, the examiner has the ability to create and search on combinations of CPC symbols (provided as groupings of symbols), each symbol in a grouping has a defined relationship to the other symbols in its grouping. These groupings are termed combination sets, and provide an enhanced mechanism for storing and retrieving classification information from patent documents. While the usage of CPC combination sets is confined mostly to the chemical fields, there are numerous instances where combination sets are used in mechanical and electrical fields.

The first symbol in a combination set is termed the base classification symbol, and determines the authorization for creation or deletion of combination sets within the field of the base symbol. The other members of a combination set possess the same Invention or Additional information, i.e. INV/ADD attribute as the base symbol, with an ordered ranking to denote their positioning within the combination set.

Guidance on the creation of combination sets is detailed in the CPC classification definitions. For example, the combination sets in a given field may denote the sequence of operations in a multi-step process, while in another field, the combination sets may denote the product and its method of manufacture. It is even possible to have the same CPC symbol appear more than once in a given combination set, with the ordering thereof to reflect the occurrence of multiple steps provided for by the repeated CPC symbol.



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Last Modified: 06/25/2020 18:23:21