Usury is a contentious issue in Catholic theology, philosophy, and economics. The notion that the Church’s authoritative teaching on the subject has changed is often used to justify arguments for changing other teachings. Defining the term usury is also a challenge, given the complexity of modern finance. We summarize recent literature on the nature and permissibility of usury and add to this literature by examining modern financial contracts in light of the Church’s last authoritative document on the subject of usury.