The Roman legal tradition is the ancestor of modern contract law but there is no agreement as to how and when a general law of contract emerged. Wim Decock’s thesis is that an important step in this evolution was taken by theologians in the sixteenth and seventeenth centuries. They transformed the Roman legal tradition (ius commune) by insisting on the moral foundations of contract law. Theologians emphasized that the enforceability of contracts is based on voluntary consent and that a contract should not enrich one party at another's expense. While their main concern was the salvation of souls, theologians played a key role in the development of a systematic contract law in which the founding principles were freedom and fairness.

Theologians and Contract Law is winner of the Heinz Maier-Leibnitz-Preis 2014 (German Research Foundation) as well as the Raymond Derine Prijs 2012 (Raymond Derine PhD Prize) and the ASL-Prijs Humane Wetenschappen 2012 (ASL Award for Humanities 2012) by the Academische Stichting Leuven. Decock's book is also awarded the "Juristisches Buch des Jahres" (Law book of the year) by Neue Juristische Wochenschrift (47/2013: 3420).