Many researchers mistakenly think that 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. Older patents do not have as many online search options because the patent pages were put into the USPTO database as scanned images.
If you know the PATENT NUMBER:
The patent number is the magic key to the patent information system. Because patent numbers are often found on manufactured objects, collectors often use patent numbers to find information relating to a particular antique object. Regardless of what date the patent was issued, if you know the patent number, you can quickly pull up the full-text patent by searching Google Patent Search (using the box to the left), the US Patent & Trademark Office site, or the pat2pdf website. Almost all free sites will allow you to enter a U.S. patent number and retrieve a PDF version of the patent.
If you do not have a U.S. patent number and want to search through the patents by topic or inventor, options vary depending on how far back you want to search:
For patents issued after 1975, go to either the Google Patent or Espacenet website to search and obtain the full text of the patent(s) regardless of whether you want to do a subject or assignee search.
For patents issued in 1975 or before, search options are more complicated. U.S. patents issued from 1790 through 1975 are only searchable from the USPTO website by Issue Date, Patent Number, and Current US Classification. Google Patent Advanced Search screen will allow you to search by patent number, inventor, assignee, topic,classification number, and date. Once you have a search result, you can also refine it using "Search Tools" to limit search by issue date, publication date,patent office, filing status, and patent type.
If you know the PATENTEE or ASSIGNEE:
Search either Google Patent or Espacenet by keyword (seethe Free Patent Websites tab on this guide for more details). Google Patent will allow you to specify the "field" you want it to search in but only if you use the Advanced Search screen.
If you know the SUBJECT OF INVENTION:
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: