An amercement is a financial penalty in English law, common during the Middle Ages, imposed either by the court or by peers. The noun "amercement" lately derives from the verb to amerce, thus: the king amerces his subject, who offended some law. The term is of Anglo-Norman origin (Law French, from French, from Latin), and literally means "being at the mercy of": a-merce-ment (English mercy is cognate).

While it is often synonymous with a fine, it differs in that a fine is a fixed sum prescribed by statute and was often voluntary, while an amercement is arbitrary. Amercements were commonly used as a punishment for minor offences (such as trespassing in the king's forest), as an alternative to imprisonment.