Classification

Brainstorm keywords related to the purpose, use and composition of the invention.

Look up the words in the Index to the U.S. Patent Classification to find potential class/subclasses.

Verify the relevancy of the class/subclasses by using the Classification Schedule in the Manual of Classification.

Read the Classification Definitions to verify the scope of the subclasses and note "see also" references.

Access Full-Text 

Search the Issued Patents and the Published Applications databases by clicking here. You can search by keyword, inventor/assignee name, or classification. 

Review and References 

Review the claims, specifications and drawings of documents retrieved for relevancy.

Check all references and note the "U.S. Cl." and "Field of Search" areas for additional class/subclasses to search.

More information on A Seven Step Search Strategy with Detailed Examples - prepared by the USPTO.

Depending on the database and the age of the patent, often there are few, if any, keyword fields (title, abstracts, indexing). For example, U.S. patent records in the USPTO database prior to 1976 can only be retrieved by issue date, patent classification codes, and patent number. Hence, to do the most comprehensive search possible, one must identify classification codes for the topic of interest. However, a searcher faces three major challenges:

1. Classification systems are very detailed and extensively hierarchical.
2. Given the level of detail, multiple classification codes are usually assigned to a patent, each designating a particular aspect of the invention. Hence, the full invention is often described only by a combination of codes.
3. Historically, there were three major classification systems: the U.S., ECLA (European Patent Office), and International Patent (IPC) systems. Fortunately, a new system, the Cooperative Patent Classification (CPC) system has been developed. As of 2020, patents from at least 29 countries/offices are participating in the CPC. This includes U.S. patents back to 1836, many European countries, China, World (PCT), and Japan. It is expected that eventually, nearly all patent offices will adopt the CPC system. The ECLA and the U.S. Patent Classification systems have been completely replaced by the CPC already.

The good news is that all the classifications systems have an easily searchable/browsable free online database.

• CPC Patent Classification  |  Browse  |  Search
• U.S. Patent Classification System  |   Browse  |  Search |  Keyword Index
• International Patent Classification System

Whenever possible, it is recommended that CPC codes be searched. The CPC is much more up-to-date and detailed compared to the other two systems. Often the best strategy is to retrieve patents with a good keyword search and then examination the description of the classification codes assigned to the most relevant patents. Finally, do a second search using some combination of the most relevant codes.

For more information about the CPC system, see CPC FAQs and CPC About Information.

• Seven-step U.S. patent search strategy (U.S. Patent Office)
• How to Conduct a Preliminary US Patent Search: A Step by Step Process (U.S. Patent Office)