There are many kinds of patent publications, and understanding what kind of document you are looking at is key. The publication number on the first page of every document is not only a unique identifier, but also provides important context. It consists of a country code, a number and a kind code:

Country code

The first two letters of the patent number identify the jurisdiction. These two-letter country codes make it easy to identify where a patent document originates. They're based on the ISO 3166-1 alpha-2 standard by the International Organization for Standardization (ISO). The World Intellectual Property Organization (WIPO) officially adopted these codes in the 1970s as part of efforts to harmonize international intellectual property documentation.

Some codes may seem unintuitive at first glance since the codes are based on the country's name in its native language or from historical designations. For example, Germany uses DE (from "Deutschland") and Spain uses ES (from "España").

Certain codes represent regional or international organizations rather than individual countries. The most important ones are:

• EP - European Patent
• WO - World Intellectual Property Organization (used for PCT international applications)

For further reading on European Patents and PCT applications, we recommend our article: There is no world wide patent.

Number / Unique identifier

After the first two letters, there is a sequence of numbers. This number mainly serves the purpose of making the publication number a unique identifier. Some offices use consecutive numbering, other offices combine a consecutive numbering with a year, which may correspond to the filing year or the publication year. Patent numbering systems vary significantly across jurisdictions, reflecting different administrative traditions and historical developments.

The USPTO uses a straightforward consecutive numbering system that has been running since 1836. Patent numbers are simply sequential integers without year prefixes. For example, US 11,234,567 B2 is a granted patent. In 2001, when the USPTO began publishing applications, they introduced a year-based format for application publications: US 2023/0123456 A1 indicates an application published in 2023.

The EPO uses a 7-digit sequential numbering system. Numbers started at 0000001 in 1978 when the EPO began operations. For example, EP 3 456 789 A1 is a typical European application number.

PCT international applications follow the format WO 2023/123456 A1, where the year corresponds to the publication year, followed by a 6-digit sequential number reset annually.

Japan's system incorporates the Japanese calendar era. For example, a patent filed in 2023 might have the format JP 2023-123456 A, where the first four digits represent the year. Historical Japanese patents may use era names (like Heisei or Reiwa) in their internal numbering, though international publications typically use the Western calendar year.

Chinese patent numbers embed both the year and a check digit at the end of the number which is separated from the rest by a dot. For example CN 202310123456.7 A is a patent application from 2023 with check digit 7.

Germany is a special case since they embed the type of document directly into the number. The format since 2004 is DE tt yyyy nnnnnn, where tt is a two-digit type code, yyyy is the filing year, and nnnnnn is a sequential number. The most important type codes are:

Type code	Description
10	German patent application
11	PCT patent application entering the national phase
20	Utility model application
21	Utility model derived from a PCT application
50	German part of a European patent (procedural language: German)
60	German part of a European patent (procedural language: English or French)

For example, DE 10 2023 123 456 A1 indicates a German patent application filed in 2023, while DE 60 2019 045 678 T2 would be the German translation of a European patent that was filed in English or French. Similar to Chinese numbers, German application numbers (called "Aktenzeichen") include an additional check digit at the end. However, when the document is published, this check digit is omitted from the publication number. So an application filed under DE 10 2023 123 456.7 would be published as DE 10 2023 123 456 A1.

Kind codes

The last part of patent numbers is the kind code, which provides information about the type and status of the patent document. The specific codes vary slightly between patent offices (like the USPTO, EPO, and WIPO for PCT applications).

The A Series generally indicates a published patent application. As described in "So why patents? What's the deal?", patent applications are being published by the patent office 18 months after filing. This first publication has a publication number with the following format:

• EP 3 456 789 A1 - European patent application
• US 2023/0123456 A1 - US patent application publication
• WO 2023/123456 A1 - PCT international application

This publication of the patent application has the kind code A, and comprises the text that was initially filed by the applicant. It does not represent the outcome of the examination procedure. One could regard the publications with the kind code A as a desired scope of protection, which is usually broader than what is granted after the examination. Thus, the A publications have the function of informing the public about the maximum possible scope of protection if a patent is granted at a later stage.

Typically, the applicant must narrow the scope of protection during the examination procedure. For that purpose, the applicant may only use fallback positions that have been part of the application documents that were originally filed as a patent application. That limitation ensures legal certainty, because the scope of the granted patent should not go beyond the subject matter of the A publication.

The B Series typically indicates a granted patent. This signifies that the patent office has examined the application and found the invention to be patentable. For Freedom-To-Operate (FTO) purposes the B publications are typically more relevant, because the claims of the granted patent define the actual scope of protection. The kind code of the publication number enables a quick determination if the document at hand is a granted patent or not:

• EP 3 456 789 B1 - Granted European patent
• US 11,234,567 B2 - Granted US patent (with prior application publication)

When trying to understand the risk of patent violations it is important to understand if you are looking just at the desired scope of protection (the A publication) or if you are looking at a granted patent (the B publication).

The number of the kind code indicates the stage of publication. "1" usually signifies the first publication of that type, while other numbers might indicate republications or corrections.

In summary, the following list gives a comprehensive overview of the most important kind codes of the major offices:

European Patent Office (EPO):

• A1: European patent application published with a European search report.
• A2: European patent application published without a European search report.
• A3: European search report published separately.
• B1: European patent (granted).
• B2: European patent with amended claims.
• B3: European patent after limitation procedure.

United States Patent and Trademark Office (USPTO):

• A1: Patent application publication (pre-grant publication).
• A2: Republished patent application.
• A9: Corrected patent application publication.
• B1: Patent granted with no previously published pre-grant publication.
• B2: Patent granted having a previously published pre-grant publication.

World Intellectual Property Organization (WIPO) - PCT Applications:

• A1: International application published with an international search report (ISR).
• A2: International application published without an international search report.
• A3: International search report published separately.
• A4: International application published with amended claims.
• A8: International application republished with corrections to bibliographic data.
• A9: International application or ISR republished with corrections, alterations, or supplements.

Other Common Codes (Can Vary by Country):

• U: Utility model application (often unexamined).
• Y: Utility model patent (often examined).
• C: Can sometimes indicate a corrected or amended granted patent.
• T: Often used for translations of granted European Patents (e.g., in Spain, "T3").

So why exactly do I need to know this?

When conducting patent searches, you'll often encounter hundreds or even thousands of results. Being able to glance at a publication number and immediately understand what type of document you're looking at saves significant time. Instead of opening each document to determine its relevance, you can make informed decisions based on the number alone. Is it an application or a grant? From which jurisdiction? What stage of the process? These answers are encoded right there in the publication number.

During a Freedom-to-Operate analysis, you need to assess the risk of infringing existing patent rights. Here's the critical point: only granted patents (B publications) confer enforceable rights. Applications (A publications) represent potential future rights, but they may never be granted, or may be granted with significantly narrower claims. By understanding kind codes, you can immediately prioritize B publications and deprioritize or exclude A publications from your core FTO assessment. This doesn't mean applications are irrelevant, since they signal potential future risks, but knowing the difference helps you allocate your analysis time appropriately.

When diving deeper into specific patents, you will find patent families (groups of related patent applications and grants filed across multiple jurisdictions) that are often presented as simple lists of publication numbers like:

• WO 2023/123456 A1
• EP 3 456 789 A1
• EP 3 456 789 B1
• US 2024/0123456 A1
• US 12,345,678 B2
• DE 60 2023 045 678 T2

Without understanding patent numbers, this list is meaningless. With the knowledge from this article, you can instantly see: the international PCT application, the European application and its subsequent grant, the US application and its grant, and the German translation of the European patent. You know which documents define enforceable rights (the B publications), which are translations (T2), and how the protection evolved across jurisdictions.

In patent analysis, context is everything. The publication number is your first and often fastest source of that context.