Throughout the Middle Ages, the charging of interest on monetary loans, as well as the sale of sacraments, were generally considered to be special types of sins: respectively, usury and simony. The repeated condemnations of these acts suggests to the contemporary reader that they could be viewed as prefigurations of contested commodities. Relying on Thomas Aquinas’s works written in the second half of the 13th century, it is shown in this chapter that money and sacraments were indeed viewed as exchanged, though, in a sense, as traded for no price. The result is the existence, in the framework of exchange, of various situations which might be ranked according to increasing commodification: first, an absolute non-commodification for the money loan, whose price is zero due to the prohibition of the payment of interest to the lender due to the loan itself, although an indemnity can be paid for other reasons and, from an economic viewpoint, appears as a counterpart for the opportunity cost of the loan. Then, two ways of expressing a kind of commodification in dealing with the sacraments: a lexical commodification in which sacraments do have a “price”, as Aquinas mentioned, but one that is out of reach on this earth; and a partial operational commodification, again for sacraments (especially for the Eucharist through mass offerings), in which something like an exchange for sacraments takes place, not at an impossible price but according to a kind of tariff which allows the priest to live.