A tax collected on imports and some exports by the customs authorities of a country. This tax is used to raise state revenue. It is based on the value of goods called ad valorem duty or the weight, dimensions, or other criteria of the item such as its size. Also referred to as customs duty, tariff, import tax and import tariff.

In the United States, duty rates are established by Congress. The rates for imports are listed in the Harmonized Tariff Schedule (HTS) which is published by the International Trade Commission (ITC). Different rates are applied depending on the countries' trade relations status with the United States. The general rate is for countries that have normal trade relations status with the United States. The special rate is for countries that are not developed and/or are eligible for an international trade program.