The concept of natural law is pervasive in academic discussions of ethics, politics, and jurisprudence. However, it is much more difficult to unearth the influence of and relationship between natural law and modern economic theory within current scholarly dialogue. This unfortunate lacuna in scholarship is inter alia due to the facts that natural law suffers from an inherent ambiguity as to whether its foundations are religious and it lacks any rigorous scientific validation. This article defends and advances the importance of natural law for modern economic theory. In doing so, it presents the classical view of natural law as found in the work of Thomas Aquinas and addresses both its religious foundations as well as scientific evidence for its existence. Beyond offering a portrait and defense of natural law, this article discusses the specific contributions that natural law offers to modern economic theory in an attempt to imbue the latter with a more complete notion of humanity and existence.