I summarize the key points of the scholastic theory of usury following The Scholastic Analysis of Usury by John T. Noonan. Usury is the sin of taking interest on a loan without a just title. According to Scholastic moral theology, interest on loans may be justified by the extrinsic titles to damnum emergens and lucrum cessans, i.e. for losses incurred or for profits lost. Implications of this teaching are discussed with regard to other contracts, such as partnerships, the census contract, bills of exchange and “dry exchange,” insurance contracts, and the so-called triple contract. Also discussed are the changes in the practices of confessors that occurred between 1822 and 1836.