Not much escapes the intellect and imagination of the Angelic Doctor, St. Thomas Aquinas. Whether it be love, children, education, moral reasoning, happiness or the proper dispositions for human existence, St. Thomas seems an expert in all of it. Crime and criminal conduct are no exceptions to this general tendency with him. Not only does he have much to say about it, what he relates is perpetually fresh and surely the bedrock of what is now taken for granted. In this short treatise, the focus targets St. Thomas’s criminal codification – his law of crimes.Indeed the magnanimity of his crimes code is a subject matter not yet treated in any detail in the scholarly literature. While parts and pieces are covered in many quarters, the literature has yet to develop a systematic, codified examination of Thomistic criminal law. The essence of the endeavor is threefold: first, how does St. Thomas factor the nature of the human person into the concept of criminal culpability and personal responsibility; second, what types of criminal conduct does St. Thomas specifically delineate and define; and lastly, what is Thomas s view of mitigation and defense, as well as the corresponding punishment meted out for criminal conduct? This short commentary zeroes in on Thomistic Criminal Law a project which will illuminate the root, the heritage and the foundation of modern criminal codification.