Laws of nature: Galileo would not be able to patent his findings from his experiments at the Leaning Tower of Pisa. Physical phenomena: Patent law classifies physical phenomena as products of nature. Thus, if your invention occurs in nature, it is a physical phenomenon and cannot be patented. Abstract ideas: Abstract ideas are concepts like pure mathematics and algorithms. You cannot patent a formula. However, you can patent an application of that formula. Thus, while you cannot patent a mathematical formula that produces nonrepeating patterns, you can patent paper products that use that formula to prevent rolls of paper from sticking together. Literary, dramatic, musical, and artistic works: These can be Copyright protected. Inventions, which are considered not useful or possible: For example, the USPTO will not issue a patent on a perpetual motion machines; or offensive to public morality.

Although, the length of utility and plant patent protection (patent term) was previously seventeen years from the date of patent grant, utility and plant patents filed after June 8, 1995 now have a patent term of up to twenty years from the date of filing of the earliest related patent application. Utility and plant patents which were applied for prior to June 8, 1995, and which were or will be in force after June 8, 1995, now have a patent term of seventeen years from the date of patent grant or twenty years from the date of filing of the earliest related patent application, whichever is longer. Utility patents are subject to the payment of periodic maintenance fees to keep the patent in force. Patent terms can be extended under some specific circumstances. See the U.S. Code Title 35 - Patents for a full description of patent laws.

The main type of patent, a utility patent, covers inventions that function in a unique manner to produce a utilitarian result. Examples of utility inventions are Velcro® hook-and-loop fasteners, new drugs, electronic circuits, software that is tied to some form of hardware, semiconductor manufacturing processes, new bacteria, newly discovered genes, new animals, plants, automatic transmissions, Internet techniques and methods of doing business (provided physical things are involved), and virtually anything else under the sun that can be made by humans. To get a utility patent, one must file a patent application that consists of a detailed description telling how to make and use the invention, together with claims (formally written sentence fragments) that define the invention, drawings of the invention, formal paperwork, and a filing fee. Sometimes the state of the art, rather than the nature of the novelty, will determine whether a design or utility patent is proper for an invention. If a new feature of a device performs a novel function, than a utility patent is proper. According to the USPTO in 2009, there were 456,106 utility patent applications. Patent law is designed to promote innovation in "science and useful arts." It's right there in the first Article of the Constitution: in order to be patentable, an invention needs to be useful in some way. Utility patents expire 20 years from the date of filing.