There are 3 patent search engines we recommend for your primary patent searching of US patents and patents worldwide. All these searches are free.
The first patent search engine we use is Google Patents. Google Patents is easy and quick. We find it to be the most simple to use patent search site. It displays the entire collection of granted US patents back to the first patent documents of 1790, and also published patent applications. Also available are European Patent Office (EPO) patents back to 1978.
Google Patents has an Advanced Patents Search page and a Prior Art Finder search feature. You can search the full texts of US patents for keywords and classification numbers. You can download entire patents easily, and for free.
The next patent search engine we turn to is the US Patent & Trademark Office (USPTO or PTO). This official US government site is very detailed. It displays complete information on patents dating from 1976 to the present. Published patent applications (from March 2001) are included. It will also display TIFF images of all patents back to 1790. Downloading and printing these patent images is presently available one page at a time.
For the PTO we like to begin by searching with Quick Search. There is also an Advanced Search, as well as a Patent Number search. Patents of other countries are also searchable.
Another popular patent search engine is Free Patents Online. You may decide to use this site for your initial patent searching because of its user friendliness. There is a nice help center, blogs, and The Manual of Patent Examining Procedure linked to case law. It claims the “most powerful search engine in the industry” for keyword searching of its database.
Free Patents Online displays US patents back to those of 1836. It also displays European patents and applications (1978-2013), patents and abstracts of Japan (1976-2013), and World Intellectual Property Organization (WIPO) patents (1978-2013).
There are also several additional free patent search engines you may want to try:
The Lens, formerly Patent Lens, is a good source for both US and foreign patents and patent application searches.
ArchPatent has an easy-to-use interface. It allows searching of patents back to 1920 and has images of patents back to 1790. There are search tools such as Boolean logic, proximity and wildcard, keyword stemming. Also includes sorting by relevance, patent number and date. I like the layout of the search results spreadsheet which gives patent #, title, assignee, issue date and PDF image of patent. From this it is easy to select patents to view. This site also has additional features for a fee.
Patent Fetcher provides complete US Patent and Patent Application and foreign patent PDF files. The US patent files are retrieved back to the first numbered patents of 1836.
You should do a search of non-patent literature for additional prior art. This can include the following keyword searches.
For technical keyword searches you can use Google Scholar (provides broad search for scholarly literature), Scirus (said to be the most comprehensive science search engine), and Defense Technical Information Center (articles on defense subjects have lists of “descriptors”=keywords).
You can also go directly to the search sites of countries outside the US and perform a patent search using the resources of any country you choose.
The reasons you need to do a patent search are explained in Why You Ought To Perform A Patent Search Online. The methods you can use to perform a patent search are described in How to Perform A Patent Search Online. Always record the results of your searches for your reference.