Custom duties are a form of tax assess and border crossings or ports between trading nations. Comparative advantage is responsible in part for the imposition of duties at the port of entry. This, in order to balance the prices of domestic production and foreign imported goods of the same item. These protective measure have been debunk over the years as trade becomes more globalized and countries become more specialized in producing competitively.

The Harmonized Tariff System (HTS) of the United States provides duty rates for virtually every item that exists.