Non-tariff barriers to trade (NTBs) are trade barriers that restrict imports but are not in the usual form of a tariff. Some common examples of NTB's are anti-dumping measures and countervailing duties, which, although called non-tariff barriers, have the effect of tariffs once they are enacted.
Some of non-tariff barriers are not directly related to foreign economic regulations but nevertheless have a significant impact on foreign-economic activity and foreign trade between countries.

Different types of Non-tariff barriers:
There are several different variants of division of non-tariff barriers. These are –

1. Licenses
The most common instruments of direct regulation of imports (and sometimes export) are licenses and quotas. License system requires that a state (through specially authorized office) issues permits for foreign trade transactions of import and export commodities included in the lists of licensed merchandises. Product licensing can take many forms and procedures. The main types of licenses are general license that permits unrestricted importation or exportation of goods included in the lists for a certain period of time; and one-time license for a certain product importer (exporter) to import (or export).

2. Quotas
Licensing of foreign trade is closely related to quantitative restrictions – quotas - on imports and exports of certain goods. A quota is a limitation in value or in physical terms, imposed on import and export of certain goods for a certain period of time. This category includes global quotas in respect to specific countries, seasonal quotas, and so-called "voluntary" export restraints. Quantitative controls on foreign trade transactions carried out through one-time license.
A quota can be a tariff rate quota, global quota, discriminating quota, and export quota.

3. Embargo
Embargo is a specific type of quotas prohibiting