"Some Members of Congress have expressed interest in the rules governing patentable subject matter for many years. The term 'patentable subject matter' refers to the requirement of section 101 of the Patent Act of 1952 that an invention must consist of a 'process, machine, manufacture, or composition of matter' in order to be patented. Most recently, the Leahy-Smith America Invents Act (AIA) of 2011 stipulated that 'no patent may issue on a claim directed to or encompassing a human organism.' The AIA also limited the availability of patents claiming tax avoidance strategies. The courts and the U.S. Patent and Trademark Office (USPTO) have historically understood the language of section 101 to allow an expansive range of patentable subject matter. However, the courts have long held that several implicit exceptions exist to the four categories of patentable subject matter set out in section 101. In particular, laws of nature, natural phenomena, and abstract ideas have been held to be unpatentable."
CRS Report for Congress, R44943
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html