A patent for an invention is a grant of property right by the U.S. government to the inventor (or his heirs or assigns), acting through the Patent and Trademark Office. The assignee of the patent has the right to exclude others from making, selling, or using the invention for a limited period of time, usually 20 years from the time of application. This right extends throughout the United States and its territories and possessions. It is important to remember that what is granted is not the right to make, use or sell the invention, but the right to exclude others from making, using, or selling the invention. Patents represent the latest advances in technology and as such are indicators of the leading technology in any field and are an excellent resource for researchers.
The inventor; the person to whom the patent has been granted. As a piece of intellectual property a patent is considered a property right and can be bought, sold, willed to heirs, etc. The patentee is not necessarily the assignee of the rights to the patent.
The recipient of the patent rights. The assignee may be a U.S. or foreign company or individual of the U.S. or a foreign government. The assignee is not necessarily the inventor of the invention being patented. Many inventors assign the rights to their inventions over to other individuals or institutions.
The Patent and Trademark Office (PTO) has developed a system of classification so that a patent can be located by its "subject" matter: what a device does, what composition a chemical has, etc. The system consists of over 400 CLASSES and 100,000 SUBCLASSES which are continuously being revised to reflect the changing technologies. It is very important to have a good understanding of the classification system in order to be able to conduct a useful patent search as it is the main point of access for locating patents in any particular area of technology.