Patent eligibility, or patent "subject matter eligibility," refers to the types of inventions which can be protected by a patent. The federal statute limits patentability to subject matter to what is "new and useful." 35 U.S.C. § 101.
Traditionally excluded are laws of nature, abstract ideas, and natural phenomena, but the scope of those exclusions has expanded in recent judicial decisions.
35 U.S.C. § 101 is the statutory definition of patent eligibility. The eligibility has four categories: invention—process, machine, manufacture, or composition of matter.
U.S. Supreme Court decisions in Bilski v. Kappos (2010) and Alice Corp. v. CLS Bank (2014) made it more difficult to patent computer-related inventions by expanding the exclusion from eligibility of "abstract ideas," while Mayo Collaborative Services v. Prometheus (2012) and Association for Molecular Pathology v. Myriad Genetics (2013), denied patents to life sciences under the Court's expanded view of "laws of nature." Only one additional Supreme Court decision has ever addressed patent eligibility: Diamond v. Diehr, 450 U.S. 175 (1981).
As of 2019, application of these decisions resulted in courts invalidating for patent ineligibility twice as many software patents as they sustained, and invalidating 25% more life science patents as upheld.
In 2022, prospects brightened for clarification of patent eligibility "in a case involving noisy driveshafts," because "[t]he US Solicitor General recommended [on May 24] that the justices step in to clarify how to determine whether or not an invention qualifies as one worthy of patent protection." But the Supreme Court denied cert in this case.
Patent eligibility is not to be confused -- although it often is -- with the other requirements of patentability, which are 35 U.S.C. § 102 (a patent must have novelty) and 35 U.S.C. § 103 (a patent must be non-obviousness).