A patent is a government granted right that allows the inventor to exclude anyone else from making, using or selling the invention in the country that issued the patent. The government grants this right to help encourage inventors to spend the time, money and effort to invent new products, technologies and the like.

In the United States, the term of a new patent is 20 years from the date on which the application for the patent was filed or, in special cases, from the date an earlier related application was filed, subject to the payment of maintenance fees.

When a patent expires, the invention enters the "public domain" allowing anyone to make, use or sell the invention without needing the permission or paying any royalty to the inventor. The government requires patents to expire because otherwise one person can control an entire industry if that person was the first to conceive of a type of product.

The patent law specifies the general field of subject matter that can be patented and the conditions under which a patent for an invention may be obtained. Any person who