You can search the texts or claims of patents for free at the U.S. Patent & Trademark Office (USPTO) at http://www.uspto.gov. The USPTO's system can search U.S. patents back to 1976 and U.S. patent applications back to March 2001 (when they were first published). You can also use it to make bibliographic searches -- for example, to find out the name, title of invention, or patent number -- of patents from 1790 to the present. You can easily and quickly download, view, and print the images of any patent before 1976 at the USPTO's website. For example, with a broadband Internet service, you can view and print the images of a ten-page patent in less than two minutes! Everything is free on the USPTO's website, except for orders of patents to be sent by mail.

You can also search U.S. patents and perform patent number searching of worldwide collections for free if you register at Delphion at http://www.delphion.com. ("Basic registration" is free. After registering, click "Research.") Delphion also offers more extensive searching capability as a fee-based subscriber service.

Another fee-based company, Micropatent (http://www.micropatent.com), uses optical character recognition (OCR) to incorporate the data from all patents since 1836 into its data bank. (Although the U.S. first granted patents in 1790, the patent numbering system did not begin until 1836.) While Micropatent's OCR results are not 100% accurate, they do provide the first way to search all patents on the Internet. Two other fee-based services are PatentMax (http://www.patentmax.com), a patent site that permits batch downloading, and PatBase (http://www.patbase.com), a database that can search many nations' patents back to the 1800s and permits batch downloading.