Whether you're developing a new invention or would like to learn more about a currently existing one, patents serve as a useful source of information regarding existing intellectual properties, their inventors, blueprints/schematics, when they were filed, etc.
Patents can be searched in the following databases:
Google Patents - provides access to U.S. patents from the 1790s to the present. It also includes patents from around the world that have been translated. Searchers can easily download the PDF of a patent found in the database. Instructions on how to search the database can be found here.
Espacenet - Europe's network of patent databases. Search for patent applications in their original language from the European Patent Office and the World Intellectual Property Organization (WIPO). Ways to search include title, abstract, application number, and more.