In economics, trade barriers refer to various measures, policies, or restrictions that governments or authorities put in place to regulate and control the flow of goods and services across international borders. The primary goal of trade barriers can be to protect domestic industries, ensure national security, raise revenue, or achieve other economic or political objectives.

Trade barriers can take several forms:

1. Tariffs: Tariffs are taxes or duties imposed on imported goods and services. They increase the cost of foreign products, making them less competitive compared to domestically produced goods. Tariffs can be specific (a fixed amount per unit) or ad valorem (a percentage of the product's value).
2. Quotas: Quotas limit the quantity of specific goods that can be imported during a certain period. This artificially restricts the supply of foreign products, protecting domestic industries from foreign competition.
3. Subsidies: Subsidies are financial support or incentives provided by governments to domestic industries, making their products more affordable or competitive in the global market. This can distort international trade by favoring domestic production over imports.
4. Import Licenses: Import licenses require businesses to obtain official permission before importing certain goods. This can act as a barrier by creating administrative hurdles and delays.
5. Voluntary Export Restraints (VERs): In a VER, the exporting country voluntarily agrees to limit the quantity of goods it exports to another country. This is often negotiated to avoid more restrictive measures like tariffs.
6. Technical Barriers to Trade (TBT): TBTs involve setting technical standards or regulations that foreign products must meet in order to be sold in a particular market. These standards can be used as a barrier to exclude or restrict imports.
7. Non-Tariff Barriers (NTBs): NTBs encompass various non-tariff measures that impede trade, such as bureaucratic procedures, licensing requirements, product quality standards, sanitary and phytosanitary measures, and other regulatory obstacles.
8. Currency Manipulation: Some countries may manipulate their currency's value to make their exports cheaper and imports more expensive. This gives their domestic industries a competitive advantage in international trade.
9. Embargoes and Sanctions: Embargoes and sanctions prohibit trade with specific countries for political, security, or human rights reasons. These measures can severely limit or entirely halt economic interactions.
10. Dumping: Dumping occurs when a country sells its products in another country at a lower price than what it charges domestically or even below production costs. This can harm domestic industries in the importing country.

Trade barriers can have both intended and unintended consequences. While they may protect domestic industries, they can also lead to higher prices for consumers, reduced product choices, retaliation from trading partners, and inefficient resource allocation. International efforts, like those through the World Trade Organization (WTO), aim to reduce trade barriers and promote more open and fair global trade.