A tariff refers to the duty imposed on a foreign item when it is imported into another country. It also refers to custom duties or custom tolls. Before World War II, many countries supported trade protectionism theory, the tariff in the United States reached its highest point. It became lower when free trade theory was dominant after WWII when the GATT was signed, establishing the WTO. The U.S. Customs and Border Protection is the law enforcement organization responsible for tariff classification in the United States.

[Last updated in May of 2022 by the Wex Definitions Team]