Subject matter eligibility, a foundational doctrine of U.S. patent law, defines the types of inventions that are eligible for patent protection. 35 U.S.C § 101, the statutory basis for subject matter eligibility, notes four distinct categories of inventions that are eligible: processes, machines, manufactures, and compositions of matter. However, these categories are constrained by three judicial exceptions: (1) abstract ideas, (2) laws of nature, and (3) natural phenomena. These exceptions are meant to prevent inventors from patenting the basic building blocks of scientific progress. The judiciary has attempted to mark the boundaries of these exceptions through case law since the earliest days of the American patent system. However, as technology has advanced, it has become increasingly difficult to determine whether an invention invokes one of the judicial exceptions. Four Supreme Court cases, decided between 2010 and 2014, outlined the exceptions and culminated in the Mayo/Alice test: a two-pronged approach clarifying the doctrine of subject matter eligibility. Recently, in the case of American Axle v. Neapco Holdings, the Court of Appeals for the Federal Circuit created uncertainty surrounding the Mayo/Alice test by invalidating a patent claim for a vibration-dampening liner. The court's ruling that a tangible product can implicitly invoke a law of nature could have wide-reaching implications for the doctrine of subject matter eligibility. This Comment explores the history and current state of the subject matter eligibility doctrine in the U.S. patent system. It further discusses the implications of the American Axle decision and its potential impact on the judicial exceptions. Finally, this Comment examines the American Axle decision's potential impact on the chemical and materials industries and seeks to provide guidance to practitioners in these fields regarding what they might expect moving forward. [ABSTRACT FROM AUTHOR]