in modern law, the practice of charging an illegal rate of interest for the loan of money. In Old English law, the taking of any compensation whatsoever was termed usury. With the expansion of trade in the 13th century, however, the demand for credit increased, necessitating a modification in the definition of the term. Usury then was applied to exorbitant or unconscionable interest rates. In 1545 England fixed a legal maximum interest; any amount in excess of the maximum was usury. The practice of setting a legal maximum on interest rates later was followed by most states of the United States and most other Western nations.

In some Muslim countries the charging of interest is still forbidden, at least in theory. The Qurʾān, the Muslim holy book, prohibits the charging of interest, although various methods have been devised in order to circumvent the prohibition. For instance, a higher price may be charged for goods when payment is deferred than is charged if payment is made in advance or upon delivery.