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Patents: A How-To-Find Guide

Information on locating full-text of patents granted worldwide.

Searching for Patents

How to search for patents

It is tempting to think all searching can be done electronically – and for the majority of modern patents (published after 1975) this is essentially true. Patent searchers, especially inventors who need to thoroughly search the entire realm of patents to ensure their idea hasn't already been patented, have more limited options available electronically and for free. Pre-1976 U.S. patents are often difficult to find because the patent pages were put into the USPTO database as scanned images, and full text searching was added later through machine transcription. Older patents from outside the U.S. can be even more challenging to find. Below you'll find some basic tips and strategies for locating patents.

For preliminary patent searching:

Doing a preliminary patent search is an important first step for inventors hoping to patent their new invention. The following tutorial, produced by the USPTO, details a patent-searching process that can be adapted for just about any free patent search tool.

To find patents based on the type of invention:

If you do not have a specific patent in mind and want to search for patents by subject or by the type of product or process being patented, there are several options:

Search by keyword

Keyword searching using free patent search tools may give you an idea of what is out there (or not, depending on which terms you use). You can also use this strategy to identify classification codes, inventor names, and other information you can then use to run additional searches. Keyword searching should not be your primary or only patent searching strategy if you are conducting a preliminary patent search or are doing your own prior art search.

Classification searching

This involves searching using the Cooperative Patent Classification or other patent classification system. These systems organize patents hierarchically based on what they are about or for. If you know the classification for the type of item you're interested in, you can quickly locate patents for that type of item regardless of the terminology used in the patent. This will often find patents missed by a keyword search.

Use a specialized database

Some subject-specific databases also include information on patents relevant to that discipline. You can search for your topic in these databases and then limit your results to patents. For example, you can use SciFinder to find chemical information in patents. (SciFinder requires a current ISU net ID for access.)

Finding a patent based on known information

If you know the patent number:

In many ways the patent number is the magic key to the patent information system. Regardless of when or where the patent was issued, if you know the patent number, you can nearly always quickly pull up the full-text patent. Almost all free patent searching websites will allow you to enter a U.S. patent number and retrieve a PDF version of the patent, while others also cover patents from other countries around the world.

If you know the inventor, owner, or assignee's name:

Search using Lens or Espacenet. These tools allow you to limit your search to specific fields (including assignee, inventor, owner, and so on) in the patent, rather than looking for words anywhere in the full text. This can quickly retrieve a list of patents owned by a particular company or invented by a specific person.

Searching for U.S. patents

The steps listed in the General steps tab will all work for U.S. patents. However, there are some additional quirks and strategies to be aware of when searching for U.S. patents.

The source of record for patent information is the U.S. Patent and Trademark Office search tool.

If you know the U.S. patent number:

You can enter the patent number in Google Patents to quickly retrieve the full text.

If you do not know the U.S. patent number:

You can also search for patents by topic or inventor, but options vary depending on how far back you want to search:

For patents issued after 1975:

Patents issued after 1975 can be easily searched by keyword. This will search in specific fields like the assignee, as well as the full text of the patent. See the links above or the Patent Search Engines page of this guide for more details on how to search by topic or inventor.

For patents issued in 1975 or before:

Search options are more complicated, but improving, for older U.S. patents. Many early patents are now full-text searchable, although the digital texts were automatically machine-generated and may contain gibberish or errors, making them sometimes difficult to search using keywords.

The following tools offer options for searching for older U.S. patents, though their records may contain errors.

If you know the date the patent was issued:

If you know the date the patent was issued or published, it is often fastest to go directly to the USPTO's Patent Public Search and use one of the date-searching options detailed below.

Publication dates

Format searches as follows to search by publication (issue) dates, replacing YYYY with the year, MM with the number of the month, and DD with the number of the day.

  • Exact publication date: @pd=YYYYMMDD
  • Publication year: @py=YYYY

Filing dates

Format searches as follows to search by application (filing) dates, replacing YYYY with the year, MM with the number of the month, and DD with the number of the day.

  • Exact filing date: @ad=YYYYMMDD
  • Filing year: @ay=YYYY

Note: There are currently many irregularities with date-searching in Patent Public Search. If you cannot find what you are looking for, or if you want to search a range of dates, try the Lens Patent Search.

Find more information: Gazette of the U.S. Patent Office

If the information you have is limited and is not getting you to the patent document, try looking in the Gazette of the United States Patent Office. These hefty volumes listed information about all the patents granted in a given time period, including inventor names, patent numbers, and issue dates—all key information for locating the document. Volumes of the Gazette are now viewable and searchable online via HathiTrust and can help supply the bibliographic information (such as patent number or publication date) needed to get to the patent document.

Unnumbered patents

Very early U.S. patents, published from 1790 to 1836, were not assigned patent numbers and can be very challenging to locate because they lack this important information for searching. These patents are included in the USPTO database, and the ISU Library also has a copy on CD-ROM.

Obtaining full-text

Researchers should be able to obtain full-text copies of most U.S. patents through either Google Patents or the USPTO website. U.S. patent applications granted since March of 2001 can also be found on the USPTO website. Full text of patents from around the world can often be obtained from tools like Lens or Espacenet.

When all else fails...

Patents that are not available through these resources may be obtained through Interlibrary Loan (ILL) at no cost to ISU faculty, staff, and students, or those with an ISU Visitor Card (some exceptions apply). Regular service takes 3-5 days. Some fees may apply. Please have the country and patent number available when requesting through ILL.

Plant patents

Plant patents are a bit different. The original paper version of the patent will show plant images in color; however, most websites only show a black & white scanned version with no color. If you need a plant patent and want the color version: check the University of Maryland's Plant Patents Image Database; visit the nearest patent depository library (in Iowa this is in the Davenport Public Library); or request a color scan through Interlibrary Loan.

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Heather Lewin
150 Parks Library
(515) 294.1004