There are several different ways of doing online free patent search on the web. Online free patent search is important to determine if the invention is patentable. The online free patent search was originally limited to the Patent and Trademark Office database records of prior patents and publications. But with the aid of the Internet and the recognition of business method patents, online free patent search is evolving and becoming easier to do. But still, online free patent search begins in the electronic databases of the various Patent Offices worldwide.

One can find detailed information and links to the various patent web sites on the S&E Finding Patents web page. The two major online free patent search web sites recommended by the S&E library are the Delphion Intellectual Property Network and the United States Patent and Trademark office (USPTO). The Delphion site is an online free patent search that contains a database of complete patents from 1974 until the present in an image format, plus some patents issued during 1971-1973. The U.S.P.T.O online free patent search database starts from 1790 to present and provides the full image of each patent as well as bibliographic data and "front-page" information. The U.S.P.T.O online free patent search allows use several different fields making this the ideal database for in-depth US patent number search pertaining to the invention.
The following tasks are necessary in conducting US patent number search:

1. Select an appropriate patent web site
2. Recognize a patent number
3. Search by US patent number search at the Delphion Intellectual Property Network or conduct US patent number search at the USPTO web site
4. View the results of your US patent number search
5. Order copies of the patent

The inventor need not approach a patent counsel to conduct online free patent search. They can do the work themselves and search for online free patent search sites. Aside from Delphion and USPTO, an inventor may also conduct online free patent search through the Patent and Trademark Depository Library (PTDL). PTDL is a library which is designated by the US Patent and Trademark Office (PTO) to receive and house copies of US patents and patent and trademark materials, to make them available to the public, and to disseminate both patent and trademark information. To be designated, a library must meet specific requirements and promise to fulfill certain obligations. Patents and trademarks (word marks only) may be searched at the PTDLs. Patent and Trademark Depository Librarians cannot give any legal advice nor can they perform the online free patent search for you