Assorted trade barriers also affect global marketing. These barriers fall into two major categories: tariffs—taxes levied on imported products— and administrative, or nontariff barriers. Some tariffs impose set taxes per pound, gallon, or unit; others are calculated according to the value of the imported item. Administrative barriers are more subtle than tariffs and take a variety of forms such as customs barriers, quotas on imports, unnecessarily restrictive standards for imports, and export subsidies. Because the GATT and WTO agreements (discussed later in the chapter) eliminated tariffs on many products, countries frequently use nontariff barriers to boost exports and control the flows of imported products.