Cooperative Patent Classification Primer

Patent classification information tells you a lot about a patent including:

The CPC and Finding Stuff

The Cooperative Patent Classification (CPC) is now the classification system of choice at USPTO, EPO and other national patent offices. There's lots of information out there but we needed something more concise to help us work with it.

Here is a compilation of information on the operation and implementation of the Cooperative Patent Classification System (CPC). These are the notes we put together to understand what's going on with the new classification scheme. We hope they will help you as you dive into the new world of the CPC.

Indicates our commentary and clarification, and more.

What to Look For When Classifying

Or what to think about when trying to find stuff and figure out what classification(s) is likely to be used for a patented invention.

The classifier should identify the following:
All of these elements are useful in allocating class symbols using the CPC.

Allocating symbols is patent-speak for deciding which classifications are assigned to a patent or patent application.

Subject Matter

The correct definition of the subject matter is essential to identifying the right classes for the invention. The subject matter is typically related to an element or elements (a thing) and its environment (how the thing interacts with its environment). Is it the thing itself or its interactions with the environment that add to the art. ( Add to the art means be worthy of a patent because the thing or a things interaction with the environment is novel, useful, and patentable.) The "thing" is a core invention but a "thing" is not necessarily a physical thing. ( Think about software when it’s running - you don’t really think about that as a "thing")

Physical Entities


Consider the implementation of a thing:

Some classes focus on the function while others focus on particular applications.

Thing Relationship
Subject matter per se Relationship with the environment
Function of "the thing" Application of the thing
Intrinsic features Particular use
Orthogonal elements Process, application, composition
entity activity
physical entities activities
two subcategories
apparatuses (or devices) and Products
method of use
In the chemical domain - compound: A chemical compound is a substance formed of atoms attached to each other via chemical bonds. In the chemical domain = composition. A chemical composition is a product formed from two or more discrete chemical materials (compounds and other elements) which are not chemically bound to each other.
An alloy is usually a composition but may in some instances be a compound. (An alloy is a metal made by combining two or more metallic elements, esp. to give greater strength or resistance to corrosion : an alloy of nickel, bronze, and zinc.)

Function-Oriented CPC Classification

Technical features necessary for defining the novel, nonobvious solution to a problem, and which represent the contribution over the prior art, are specific to a particular application. It should be classified in the Application-oriented CPC place.

The examination of the file will be influenced by the categories of the claims, since the scope of the protection sought is also determined by these categories.

Considerations apply in relation to processes in products:

Process-Oriented CPC

Multistep Processes

Try to find a single CPC class that covers the invention as a whole - unless it’s clear that the subject of the invention concerns a particular element of the combination.

Beware of Classification Buckets

The CPC seems to have lots of "buckets" - "This subclass covers only single or combined, (multistage) operations not fully classifiable in a single other subclass."

Notes on Inventions in the Chemical Domain

Function vs. application — the "thing" is the chemical substance - compound or composition.


Types of Classification

There are two types of information used for classification:

Inventive Information — Technical information that represents the addition to the state of the art. Novel and unobvious subject matter. It should answer the question about the invention, "What is the addition to the state of the art?"

Inventive information appears on the patent image in BOLD ITALICS.

Additional Information — Valuable information about the document whose presence might be interesting in further searches. Additional Information is technical, does not add anything to what is already known in the art — not new but not trivial. Additional Infomation groups provide an entry for an aspect of the classification that classifiers in the field have found useful for a search but which does not have enough weight to conform an invention by itself.

Additional information appears on the patent image in light italics.

Invention information Additional information
Novel Not new
Unobvious Not trivial

Patents have one of the more unusual uses of the word obvious, the creation of its opposite, non-obvious or put another way, patents are the opposite of obvious in any given field.

In the CPC both invention information and additional information can be classified. Combination of symbols with inventive and additional info will provide "targeted, efficient" search.

It is possible to allocate a symbol either as invention information or as additional information depending on the context in which is is used in the particular document.

Some classifications can only be allocated as additional information and not permitted to be allocated as invention information symbols. These codes can be identified by 20XX digit in the subclass code.

2000 series breakdown codes are used to classify a refinement or a detail specific (contextual) to the group in consideration. 2000 series orthogonal codes are used to classify a refinement or a detail not specific to the group in consideration, i.e. crossing over (going orthogonal to) more main groups.

The actual policy for allocating invention information and additional information is STRONGLY FIELD DEPENDENT. Some fields use additional information extensively while other rely on invention information exclusively.

CPC definitions, a field oriented document will be an important reference. It will inform the classifier of the actual detailed practice in the specific CPC subclass.

There is no USPTO/EPO guidance on which fields use additional information extensively. You’ll just have to look for patents with bloated lists of classifications on them.

Comprehensive Classification

Comprehensive classification requires full characterization of the subject matter in the document. Requires classification of the document in all relevant areas. Completeness of classification may require the intervention of more than one specialist. Allocation of invention information symbols implies a specialized knowledge in the field (what aspects are or are not susceptible to become an invention -- the whole process implies the intervention of a number of specialists.

Classification needs to deal with the peculiarities in the specific technical area.

The completeness in classification is assured by circulating the document between the very specialized classifiers

This approach deals with convergence and scientific dispersion. ( Like phones with cameras.) USPTO commentary on the future goal of the CPC notes,

The power of an efficient paperless search tool resides in the possibility of combining a plurality of appropriate classification entries. To exploit this potential, classification needs to be correct and complete.

( Basically, it's time for the classification mash-up - searching by groups of classifications that best represent your invention.)

The CPC Scheme

How the Cooperative Patent Classification System is organized.

CPC Sections

A: Human Necessities
B: Operations and Transport
C: Chemistry and Metallurgy
D: Textiles
E: Fixed Constructions
F: Mechanical Engineering
G: Physics
H: Electricity
Y: Emerging cross-sectional technologies.

About the Classification Structure

Section  |  Class  |  Subclass  |  Group

—Section (one letter A to H and also Y)

    —Class (two digits)

      —Subclass (one letter)

        —Group (one to three digits)

          —Main group and subgroups (at least two digits)

The hierarchal subdivision of the CPC is recognizable in the structure of the name of the group.

The classification symbol is constructed in such a way that the section, class, and subclass can be easily identified.



Section   |   Class |   Subclass   |   Group

A   |  01 |  B |  22/00

A   | A01 | AO1B |A01B | A01B 22/00

CPC Definitions

There are 626 CPC Definitions (one per subclass) with an PDF and XML file for each.

( As of when we wrote this in July 2015.)

CPC definitions have eight sub-sections:

  1. Title
  2. Definition statement
  3. Relationship between large subject-matter areas
  4. References relevant to classification
  5. Informative references
  6. Special rules of classification
  7. Glossary of terms
  8. Synonyms and keywords


Another unofficial section in the definitions is the presence of a WARNING. Be on the look out for them. They can wreck your whole search experience if you don't heed them.

Patent Families and CPC Classifications

When a patent document is given a CPC classification, its family members (documents claiming exactly the same priorities) are also given the same classification. If an examiner notes that the contents of a specific document differ from those of the first document classified, the family can be rebuilt so as to allow the assignment of a different CPC classification.

Often a subclass constitutes a classification unit which is big enough; yet sufficiently homogeneous as to define a unitary technical field.

The subclass is the highest level where a document may be classified. Basically this seems to be saying dump them in the highest possible subclass symbol if they are similar, kind of alike, or if it's just too much of a pain to reclassify all those members of the patent family. This looks like another "bucket".)

Main Group is the one that ends with /00

Groups are where the indents kick in — hierarchically organized by the number of dots in the title of the group. ( A throw back to the venerable USPC.

CPC is Annotated. Annotations are characterized as:

  1. Heading Notes
  2. The References
  3. The Rules of Classification


In multipart titles which comprise two ore more distinct titles separated by semicolons, each is to be interpreted as if it stood alone.

The hierarchy of among subgroups is determined soley by the number of dots preceding their titles.

The scope of a group is limited by the scope of all hierarchically higher groups. (The stuff above and one dot less…)

Guide headings are provided if there are several successive main groups related to common subject matter. They appear before the first of such main groups coving the subject-matter.

References — phrases in braced together with a class, subclass, or group title, a guide heading or note and referring to another place in the classification scheme. References is the phrase that appears in parentheses in the title of a CPC symbol. Usually a different font and size so that it cannot be confused with the title itself.

References are used to:

Using a reference the scope is delimited by specifying the subject matter which is NOT covered here but is covered somewhere else. Without the reference the subject matter would include the within the meaning per se.

Indication of Precedence — When there is overlapping concepts the reference states which takes precedence. This is usually at the subgroup level. (Within the dots) Used to avoid dual classification.

Notes can be associated with a section, class, subclass, guide heading or group.

{  } — "Covered by" means that subject matter fits there. "Provided for" is equivalent to covered.

AND — Two elements separated by AND means they both need to be present (Thank you George Boole!!)

OR — Two elements separated by OR requires either of the two elements or both.

In General — "In general" means things considered intrinsically, disregarding application. B08B - cleaning in general.

Specifically Adapted For — "Specially adapted for" indicates things that have been modified or particularly constructed for the given use or purpose (i.e brakes especially adapted for cycles.)

(Grammar Police Alert — Need for attention to detail here, specifically and especially mean the same but USPTO explains the phrase "specially adapted for" in the guidance and then gives an example using "especially adapted for.")

(In general is at the other end of the specially adapted for continuum.)

{  } Curly brackets indicate material that is CPC only.


Notes are associated with a particular section, class, subclass, group, subgroup, heading, etc. Notes are placed AFTER the title of the relevant CPC symbol. Notes are particular to where they are found.

In the notes:

References and notes are continuously updated. ( The problem is it's not clear how this is indicated. USPTO/EPO don't seem the hang of this version control thing down yet.)

A Warning is a kind of note. A Warning directs the reader to an unusually, often temporary circumstance. Warnings are used during reclassification and where content is for the moment not complete. The warning shows other groups to consider searching while the work is ongoing.

The CPC will be revised on a monthly basis.

Orthogonal Classifications — Going Orthogonal

Actual Text on Orthogonal Entries: ( No kidding…)

…while these orthogonal entries vary enormously, but often generic concepts or problems which can be identified throughout a plurality of groups in the field are better covered by an orthogonal group…
( Huh???)

B65D37/2415 and B65D2215/02

( Orthogonal means - right angles, perpendicular. Having a set of mutually perpendicular axes; meeting at right angles; "wind and sea may displace the ship's center of gravity along three orthogonal axes"; "a rectangular Cartesian coordinate system". You're on your own with this one.

The second w/ 2215 is Additional Information. Readers can recognize orthogonal group from its coding since 2215 is in the 2X00 range.

Notes also explain classification placement rules:

Implementation History

Implementation by USPTO: — The transition period for the USPTO runs until the end of 2014. During this time:

  1. Newly filed US applications ("A" publications) will be classified in the USPC and the CPC.
  2. US patent grants ("B" publications) will be classified in either the USPC or the USPC and the CPC.
  3. CPC symbols will be printed on the front page, next to the IPC and USPC symbols.

From 2015 onwards, the USPTO will classify exclusively in the CPC (except for plants and designs).

Both the EPO and the USPTO will continue to classify in the IPC.

How Big Is This Thing?

The main trunk of the CPC scheme has about 160,000 symbols available for both invention information and additional information.

The CPC also has about 82,000 indexing codes, available for the classification of additional information only. (These are the 2XXX classes.)

These indexing codes stem from former ICO codes, IPC indexing codes and a large number of previous EPO keywords, converted to ICO.

Due to the code contained in their symbol, orthogonal entries (codes that extend over a range of CPC groups) and additional information-only codes are often referred to as "2000 codes". They are both often also referred to as "indexing codes".

"Y" contains approx. 7,300 symbols including former USPC "XRACs and Digests" used for additional information only.

Technical Aspects of Classification Symbols

  1. The higher level of detail, the more powerful the classification.
  2. Main Group is the one that ends with /00.
  3. CPC symbols keep the same digits after the "/" as their parent IPC symbol. The symbols consist of only numeric characters after the forward slash. If a group is specific to the CPC (and thus does not exist in the IPC), additional digits are appended. There can be a maximum of six digits after the "/".
  4. Subclass is often the highest level at which you can classify a patent.
  5. Codes identified by 20XX digit in the subclass code can only be used for additional information. This is also referred to as a "2000 series breakdown code".
  6. The CPC also includes a Y section for tagging emerging technologies or technologies spanning several sections of the CPC. Under subclass Y10S there is a selection of entries originating from former USPC cross-reference art collections (XRACs) and digests.
  7. "Place holder" symbols (which appear in grey) are not used for classification and search purposes – they exist only to provide a hierarchical context to the "breakdown" groups.
  8. The CPC has IPC groups of classifications and groups with no correspondence to the IPC.
  9. {  } Curly brackets — indicates material that is CPC only.
  10. Orthogonal entries to the IPC are recognizable by their name structure:
    These groups will typically have the structure [subclass] 2 ###/ 00

Technical Placement Rules:

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