Usury (pronounced /ˈjuːʒəri/, comes from the Medieval Latin usuria, "interest" or from the Latin usura "interest") originally meant the charging of interest on loans. This included charging a fee for the use of money, such as at a bureau de change. After interest became acceptable, usury came to mean the interest above the rate allowed by law. In common usage today, the word means the charging of unreasonable or relatively high rates of interest. The term is largely derived from Christian religious principles; Riba is the corresponding Arabic term and ribbit the Hebrew one. The primary focus in this article is on the Christian tradition.

The pivotal change in the English-speaking world seems to have come with the permission to charge interest on lent money: particularly the 1545 Act 'An Acte Agaynst Usurie' (37 H.viii 9) of Henry VIII in England (see book references).