It is tempting to think all searching can be done electronically – and this is essentially true for U.S. patents granted since 1976. 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, without full-text search capabilities. Older patents from outside the U.S. can be even more challenging to find.
In many ways the patent number is the magic key to the patent information system. Because patent numbers are often found on manufactured objects, collectors can use patent numbers to find information relating to a particular antique object of interest. Regardless of what date the patent was issued, if you know the patent number, you can quickly pull up the full-text patent using free tools that are available online. Almost all free patent searching websites will allow you to enter a U.S. patent number and retrieve a PDF version of the patent.
You can also search for patents by topic or inventor, but options vary depending on how far back you want to search:
Patents issued after 1975 can be easily searched by keyword using a number of free tools. This will search 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.
Search options are more complicated, but improving, for older U.S. patents. Many early patents are now full-text searchable through Google Patents, although the digital texts were automatically generated and may contain gibberish or be difficult to search.
U.S. patents issued from 1790 through 1975 may only be searched on the USPTO website by issue date, patent number, or classification code.
Google Patents Advanced Search screen will allow you to search by patent number, inventor, assignee, topic, classification number, and date. Once you have searched, you can also refine your results by issue date, publication date, patent office, filing status, and patent type.
Search using Lens or Espacenet. These tools allow you to search just the assignee or inventor field, rather than looking for words anywhere in the full text, if desired.
If you do not have a specific patent in mind and just want to search for U.S. patents by subject there are several different options: