Patents are governed exclusively by federal law (35 U.S.C100 et seq). To obtain a patent, an inventor must file an application with the PTO (the same agency that issues trademark registration) that fully describes the invention. Patent prosecution is expensive, time consuming and complex. Costs can run into the thousands of dollars, and it generally takes over two year for the PTO to issue a patent.
Patent protection exists for twenty years from the date of filing of an application for utility and patents and fourteen years from the date of grant for design patents. After this period of time, the invention fall into the public domain and may be used by any person without permission.
The inventor is granted an exclusive but limited period of time within which to exploit the invention. After the patent expires, any member of the public is free to use, manufacture, or sell the invention. Thus, patent law strikes a balance between the need to protect inventors and the need to allow public access to important discoveries.