Patents are arranged according to a classification system of more than 465 classes and over 200,000 subclasses. The Index to the U.S. Patent Classifications is an alphabetical list of the subject headings referring to specific classes and subclasses of the U.S. patent classification system. The classifications are intended as an initial means of entry into the USPTO’s classification system and should be particularly useful to those who lack experience in using the classification system or who are unfamiliar with the technology.

The classifications are to searching a patent what the card catalog is to looking for a library book. It’s the only way to discover what exists in the field of prior art. Before you begin your search, use the classifications to plot your direction. First, look for the term you feel best represents your invention. If you can’t find a match, look for terms of approximately the same meaning, for example, describing a similar function, effect, or application. By doing some homework before you begin searching, such as familiarizing yourself with the Index and locating the class and subclass numbers for terms that pertain to your invention, you’ll save time.

Once you have recorded the identifying numbers of possibly pertinent classes and subclasses, refer to the Manual of Classification, a loose-leaf USPTO volume listing the numbers and descriptive titles of more than 300 classes and 95,000 subclasses used in the subject classification of patents, with an index to classifications. This manual is also available at the Patent and Trademark Depository Libraries and at www.uspto.gov.

The classifications are arranged with subheadings that can extend to several levels of indentation. A complete reading of a subheading includes the title of the most adjacent higher heading and so on until there are no higher headings. Some headings reference other related or preferred entries.

New classes and subclasses are continuously based on breaking developments in science and technology. Old classes and subclasses are rendered obsolete by technological advance. In fact, if you have suggestions for future revisions of the classifications or if you find omissions or errors, you are encouraged to alert the USPTO. Send your suggestions to Editor, U.S. Patent Classification, Office of Documentation, U.S. Patent and Trademark Office, Washington, DC 20231.