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Patent Searching: Search Methods

This guide supplements other existing guides by emphasizing patent contents and search strategies.

Basic Search Strategies

How Patents and Patent Applications are Stored

Patents and Patent Applications are stored in their respective databases using descriptive fields.  These fields contain the following:

  • Basic identifying information including:
    • Patent & application numbers;
    • Application, issue, reapplication, and other priority dates;
    • Names and locations of applicant, inventor, & assignee; and
    • Names of examiners and attorneys;
  • Content information including title, abstract, description/specification, and claims;
  • Subject information including various classification codes;
  • Patents referenced by this patent and patents referencing this patent; and 
  • Cross references to related patents or foreign applications.

Search Options

From the above discussion, one can see that the information stored about patents is analogous to information stored for scholarly works (e.g., title, abstract, author, publication date, etc.).  Thus, searching for patents can use techniques similar to those used when searching for scholarly works.  Specifically, you can search for:*

  • a known item, such as a patent number or an author (inventor);
  • keywords used in patent titles, abstracts, or full text;
  • subjects, as identified in classification codes; and
  • citations, either forward ("cited by") or backward ("references") in time.

Caution should be exercised when using keywords to search for patents because patent language is not always aligned with common language.  Sometimes titles are incredibly nondescript - e.g., "Downhole Tool" or "Valves"; other times, the language selected is more technically or legally slanted than one would normally expect to use in common discussion - e.g., "Method and apparatus of assessing downhole drilling conditions."  This is because the legal aspects of patents force a rigor on descriptive language that sometimes feels unnatural. Thus, using "subject" searches with classification codes is considered a best practice for getting the most comprehensive set of relevant results.  That said, keyword searching can be useful for identifying a starting point for your classification codes, or for broadening your search beyond the classification codes already found.

*US patents prior to 1976 are searchable only by issue date, patent number, and current US classification

Search Strategies

When searching for patents in a particular subject area (not a known item), a recommended strategy is as follows:

  1. Brainstorm words that describe the key features of the invention/technology you are searching for;
  2. Search the classification system for the classification codes most closely describing the invention/technology;
  3. Look within the classification hierarchy for broader and narrower classification codes that may describe the invention/technology equally well or better; and
  4. Search for patents and patent applications that are classified according to these codes.

Note that patents and applications are often classified according to multiple classification codes.

Once a relevant patent is identified it is particularly effective to:

  • Review the classification codes assigned to that patent/application and use any of those codes that may be relevant to your subject area; and
  • Follow the citation "trail" for the patents both forward and backward in time.

If this feels like familiar territory, you are right!  These are very similar to the strategies used for searching scholarly works.


Patent Classification Systems

A Little History

Image by Emslichter from Pixabay (CC0)

Back when the world was less connected, different patent classification schemes arose, primarily including the US Patent Classification system (USPC) and the International Patent Classification (IPC), although there are others.  Each of these systems was built to provide a hierarchical (i.e., broad categories with increasingly narrow subcategories) method of categorizing patents according to the technologies represented in the patent.  This facilitates searching for patents in a particular domain.

More recently, the US Patent and Trademark Office (USPTO) and the European Patent Office (EPO) have agreed on a common classification system called the Cooperative Patent Classification system (CPC).

CPC Hierarchy Example

The following example illustrates the hierarchical structure of the CPC:

  • B60H: Arrangements or Adaptations of Heating, Cooling Ventilating, or Other Air-Treating Devices Especially for Passenger or Goods Spaces of Vehicles
  • B60J: Windows, Windscreens, Non-fixed Roofs, Doors, or Similar Devices for Vehicles;...
    • B60J 1/00: Windows; Windscreens: Accessories therefor
    • B60J 3/00: Antiglare equipment associated with windows or windscreens
    • B60J 5/00: Doors
    • B60J 7/00: Non-fixed roofs; Roofs with movable panels
      • B60J 7/02: of sliding type
      • B60J 7/08: of non-sliding type, i.e. movable or removable roofs or panels
      • etc
    • B60J 9/00: Devices not provided for in one of main groups B60J 1/00-B60J 7/00
    • etc
  • B60K: Arrangement or Mounting of Propulsion Units or of Transmissions in Vehicles;...


Using the CPC

The USPTO website provides a handy tool for finding CPC codes for your topic.  To use this tool, go to and click on the "Patents" menu in the "Find It Fast" section of the page:

US Patent Office Home Page with Arrows pointing to Paten menu item


Then select "Classification."  This will load the lookup tool:

Classification Lookup Tool with arrows for keywords


To find the CPC codes for your topic, make sure the "All CPC" radio button is selected, and type in the keywords you brainstormed.  When you press "Search" the lookup tool will return the codes you are looking for:



Read through the descriptions in the results list and select the ones that are most relevant.  When one of the "CPC Schemes" is selected, you will then see the hierarchical classification structure:


You can choose to use CPC codes of whatever level of specificity you desire.  For example, if you are looking for patents on removable vehicle roofs, CPC scheme B60J includes non-fixed roofs for vehicles, but B60J 7/00 is the sub-class that includes specifically non-fixed roofs, so searching that subclass will save time weeding through other irrelevant items that are part of the broader class, such as windows and doors. 


Likewise, B60J 7/12 is even more specific, including foldable roofs, and B60J 7/1226 includes soft tops for convertible vehicles.