Read this section. Patent law is an increasingly complex area of law, and is filled with conflict and controversy. It creates a property right of the design of useful new inventions for a certain period, after which the patent expires. There are three types of patents; make note of what these are, and also of the kinds of things that cannot be patented. Patent holders have remedies when patents are infringed, which has led to the emergence of patent-holding companies, or patent trolls, that derive revenue solely from suing for patent infringement. Be sure to complete the exercises at the end of the section.