Patent classifications

Overview
U.S. patents are classified according to both a domestic and international classification systems. Issued patents are classified to make it easier for the public to search the Patent Office records, and to allow patent examiners to search for prior art when processing future patent applications.

The Patent Office provides a concordance between the domestic and international classification systems.

Domestic classification
The domestic classification system is administered by the Patent Office. The code includes two numbers separated by a slash mark. The first number designates the class and the second number the subclass. The first U.S. classification code is printed in boldface and is considered the "original" or primary classification of the patent. The remaining classifications are considered cross-references.

International classification
The international classification system is administered by the World Intellectual Property Organization (WIPO) under the 1971 Strasbourg Agreement Concerning the International Patent Classification.

The international classification code begins with a letter, a number, and a second letter, which designates the section, class and subclass. The code concludes with two numbers separated by a slash mark, which defines the group.