The Cooperative Patent Classification (CPC), explained

What the CPC is

The CPC is a joint EPO and USPTO system, announced in October 2010 and based largely on the EPO's old ECLA scheme, adapted to stay compliant with WIPO's International Patent Classification (CPC: About). The USPTO replaced its own US Patent Classification with the CPC on January 1, 2013 (USPTO). The EPO describes it as an extension of the IPC with approximately 250,000 classification entries.

It is revised several times a year. In 2026 new versions came into force on January 1, May 1 and August 1; version 2026.08 is current. Revisions create, split and retire groups, and the offices then reclassify the existing documents, so the class on a document's front page may be out of date while the database record carries the current one.

How a CPC symbol is built

Take G06N 3/08, a code you will see on many machine-learning patents. Read from the left, each part narrows the one before. The titles below are from the G06N scheme, version 2026.08.

Three things about the subgroups catch people out.

• Dots, not digits. The number after the slash is just a position. 3/08 has two dots and sits under 3/02 (neural networks); 3/084 has three and sits under 3/08. Siblings of 3/08 include 3/04 (architecture), which holds 3/0464 for convolutional networks. A subgroup's full meaning is its title plus every title above it, so 3/08 means "learning methods for neural networks", not learning in general. General machine learning sits elsewhere, in G06N 20/00.
• Curly brackets. In the scheme, text in braces, like {Biomolecular computers...} under G06N 3/002, marks CPC-specific additions that do not exist in the IPC.
• Warnings. Newer groups are often flagged as incomplete. The current G06N scheme warns, for example, that 3/0442 (LSTM and GRU networks) is "incomplete pending reclassification of documents from group G06N 3/044", and that both should be searched. When you see a warning, search the parent group too.

The nine sections:

Inventive, additional and combination sets

A document usually carries several CPC symbols, and they are not equal. Inventive symbols describe what the invention contributes; additional symbols record other useful information, including the CPC's indexing codes (groups numbered 2000 and above, such as A61K 2039/5252). Patent Public Search lets you search them separately with .cpci. and .cpca., or together with .cpc. In chemistry and a few other areas, examiners also assign combination sets (C-sets), ordered groups of symbols that together describe, say, a mixture; search them with .cpcc. in Patent Public Search or cpcc= in Espacenet.

CPC vs IPC

In practice: search CPC when the collection has it (US and European documents, and much of the worldwide data in Espacenet), because it is finer. Fall back to IPC for offices that only assign IPC, such as IP India, and for older documents. Because the CPC is built on the IPC, the IPC symbol at main-group level is usually a safe common denominator. WIPO publishes the IPC and tools such as IPCCAT, which suggests IPC symbols from text.

The Y section

Section Y does not exist in the IPC. Its notes say classes Y02 and Y04 are only used to tag documents already classified elsewhere, to follow new technologies that cut across several sections, and that the tags never replace the main classification. Y02 covers technologies for mitigating or adapting to climate change, in the framework of the Kyoto Protocol and the Paris Agreement. Y10 holds subjects carried over from the old US classification. Some examples from the Y02E scheme and the section scheme:

Y tags are excellent for landscaping, for example every battery storage patent whatever its main class, and weak for novelty searching, where you want the precise technical group. Use them together with keywords, not instead.

How to find the right CPC class

1. Start from a known relevant patent. Run a quick keyword search, open the two or three closest documents and list their CPC symbols. Inventive symbols first. This is the fastest route, and the one the USPTO's multi-step search strategy builds on: search keywords, read the closest documents, then expand with CPC.
2. Confirm in the scheme. Look each symbol up in the official CPC scheme and definitions (or the USPTO's CPC browser). Read the titles above it, the definition's scope notes and its references to other groups, which often point to where the neighboring subject matter lives.
3. Search the scheme by keyword. Espacenet's Classification search lets you type a term, browse the matching groups and send symbols straight into a query. The CPC website and The Lens's Classification Explorer do the same.
4. Use the AI suggesters. Espacenet links to the EPO's CPC text categoriser, which suggests symbols from a plain-language description (release 1.47.3), and Google Patents suggests CPC codes as you type in its Search Terms box. Treat both as candidates to check in the scheme.
5. Check the distribution. After a keyword search, Espacenet's CPC filters and Google Patents' classification groups show which codes your hits cluster in. A class you had not thought of that holds a third of your best results deserves its own search.

Pick the level deliberately. A main group like G06N 3/00 is safe but broad; a deep subgroup is precise but misses documents classified one level up. A common approach is a narrow subgroup with loose keywords, and a broader group with tighter keywords.

Searching by CPC in each database

Patent documents print the symbol with a space (G06N 3/08). Databases want it without one, and each has its own way of including the subgroups below.

• Patent Public Search: the USPTO's searchable indexes describe .cpc. as matching current inventive and additional symbols, with range searching at subgroup level (the USPTO's example is C07C51/43-64.cpc.). To be sure of covering the subgroups under a group, list them with OR or use .cpcl. for the subclass with tight keywords. Full walkthrough in our Patent Public Search guide.
• Espacenet: the pocket guide says classification data is auto-posted to group level, so a main group finds its subgroups; at subgroup level, /low adds the lower subgroups, with = and one symbol per field. See how to search Espacenet.
• Google Patents: per its help, a CPC typed as a keyword includes all child codes, CPC= matches exactly, and CPC=.../low adds children. Its classification also extends to Scholar documents, which Google has machine-classified. More in our Google Patents guide.
• The Lens: its classification help says it indexes documents only at group level and only in the group they are filed in, not parent groups, so use a trailing wildcard to sweep subgroups and escape the slash.

For how to combine a class with keywords and proximity in each syntax, see our guide to patent search Boolean operators.

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