This new critique of Aquinas's theory of natural law presents an incisive, new analysis of the central themes and relevant texts in the Summa Theologiae which became the classical canon for natural law. Professor Lisska discusses Aquinas's view of ethical naturalism within the context of the contemporary revival and recovery of Aristotelian ethics, arguing that Aquinas is fundamentally Aristotelian in the foundations of his moral theory. The book looks at the historical development of natural law themes in the twentieth century, and in particular demonstrates the important connections between Aquinas and contemporary legal philosophers. The book should be of considerable interest to scholars of jurisprudence as well as philosophers.