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Patents and Trademarks: On Patent Searching

A service of the Patent & Trademark Resource Center at Vanderbilt University in Nashville, Tennessee

Types of Searches

Three types of searching for conducting a prior art search:

  • Keyword
  • Classification
  • Citation

Thorough searches make use of all three. One might begin with a keyword search, then follow through by searching the classification codes and cited references contained in the relevant results of the initial search. As with all research, patent searching is an iterative exercise, using information found in one search to help expand or focus a subsequent search.

Keyword Searching

keyword search can be a useful way to start patent research. Keep in mind that the language in patents is often an amalgam of technical and legal argot. Because there is no standard that governs the vocabulary used in patent documents, it can be helpful to generate a variety of keywords before beginning the search. The following questions may help with brainstorming concepts and terms based on the different aspects of an invention:

  • Is the invention a process or is it a product? 
  • What is the physical composition of the invention? (e.g., is it a new alloy or chemical compound?)
  • How is the invention intended to be used?

Avoid broad and generic terms such as "device," "process," "system," etc. Such terms will tend to bloat your results.

Classification Searching

Patent classification schema organize patents into groups of similar technologies. In a granted patent, the examiner-assigned classification codes can be used to search for patents in the same or related technology areas. A classification search is a much more focused way of searching for patents in a given field than by fishing with keywords. Recently issued U. S. patents typically display classifications codes from three or more different schema--this reflects the transition from legacy to newly adopted classification systems.  

If you have a general idea of the field of the invention, you can look it up in the Cooperative Patent Classification scheme using USPTO's website search box. It's important to preface your search terms with "cpc scheme":

There is also a CPC search tool on Espacenet, the European Patent Office website.

Additionally or alternatively, Use the Index to U. S. Patent Classification to browse an alphabetical listing of concepts and to access relevant USPC schedules. Click on the first letter of your concept to see if it is listed (use the html row to make use of hyperlinking within the Index). 

If you're starting with a USPC code, here is a tool for identifying the relevant CPC codes. 

  1. Select USPC as the classification system
  2. Enter your class and subclass numbers
  3. Select "Statistical Mapping from USPC to CPC" in the Select Content field:


Citation Searching

Every patent includes a list of References Cited. This is usually a list of related patents and sometimes includes references to journal articles or other scholarly literature. When viewing the HTML version of a patent, the patent references usually appear as links so you can easily click through to read the references.

Similarly, the HTML version of a U. S. patent includes the Referenced By link to all of the patents that cite the patent you are currently viewing.

If you know the patent number of a technology of interest and the patent is dated after 1976, a keyword search for the patent number will also return all the patents which cite your patent.

Citation searching
 is an excellent way to track trends in a particular field or technology.

Resources: Reference Books

Resources: Sites

Search Non-Patent Literature for Prior Art

A Patent Miscellany