USPTO.gov contains information on all U.S. patents issued and published since 1790. Those issued before 1976 are accessible in PDF form only, and users can search for them by patent number or classification codes only. Patents issued since 1976 have their full text indexed and may be searched with keywords.
“Google Patents” is a patent search engine from Google. It goes a step further than USPTO.gov by indexing the full text of all patents. This indexing is automated through optical character recognition (OCR) technology, which is very useful, but not 100 percent accurate.
Searching for a particular patent using a patent number can be very simple. Searching for patents that may represent prior art on an inventor’s idea is more nuanced and challenging. USPTO.gov outlines a “Seven Step Strategy” for successful searches of this type.
The World Intellectual Property Organization (WIPO) website has a patent search function as well. Also, many large cities have Patent and Trademark Depository Libraries (PDTL), which are public libraries designated by the USPTO to receive patents and trademarks and disseminate information about them.