Federal Commerce Department

A simple boolean search interface to the official patent database. Advantage: Unlimited results and free. Patent applications. Disadvantage: Limited data before 1975. US patents only. Clumsy search interface.

This site indexes US, European, and Japanese patents. The user is able to sort patents by the relevancy of the results to search terms used, which cannot be done on the USPTO site.

A free site for patents from Europe, Japan and the World Intellectual Property Organization made available from the European Patent Office. Also has some US patents and US patent applications. Allows international classification searches.

Patents from the United States Patent and Trademark Office (USPTO) searchable through Google. Advantage: Better information on older US patents than the USPTO.