To understand what patent infringement is, and why and how patent infringement occurs, one needs to first look at the history of U.S. patents and how they came into existence.

The concept for U.S. patents was established by the founding fathers in Article I, Section 8 of the original U.S. Constitution that was adopted in 1787.

It gives Congress the power to "promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."

Since patents were included in the original version of the U.S. Constitution, patent rights are actually older than such other basic American rights, such as freedom of the press and freedom of speech -- rights that were not established until the adoption of the Bill of Rights (the first 10 amendments to the Constitution) in 1791, 14 years later.

A U.S. patent is a limited monopoly granted to an inventor by the federal government for his or her invention. A patent gives the patent owner (or "patentee") the right to exclude others from using his patented invention without his or her permission.

U.S. patents are governed by the federal law known as 35 U.S.C. (United States Code). According to Section 271 of that law, patent infringement occurs when an entity -- usually a business -- "makes, uses, offers to sell or sells" a product or service that uses a patented invention.

Permission to use a patent is given in the form of a license. The patent is licensed to a manufacturer, for example, and in return the manufacturer pays the patent owner a royalty based on unit sales, dollar sales or some other criteria.

The other option is for the patent owner to sell the patent, and patents can be bought and sold just like any other asset.