A tariff is a tax placed on imported and/or exported goods. A revenue tariff is set with the intent of raising money for the government. A protective tariff, usually applied to imported goods, is intended to artificially inflate prices of imports and "protect" domestic industries from foreign competition. The distinction between protective and revenue tariffs is moot; revenue tariffs offer some limited protection, and protective tariffs produce some small revenue. Tariffs are similar to tolls, which are applied to people rather than goods.
Tax, tariff and trade rules in modern times are usually set together because of their common impact on industrial policy, investment policy and agricultural policy. A trade bloc is a group of allied countries agreeing to minimize or eliminate tariffs against trade with each other, and possibly to impose protective tariffs on imports from outside the bloc.
If a country's major industry collapses due to foreign competition, the loss of jobs and tax revenue can severely impair that country's economy. Protective tariffs have been used as a measure against this possibility. However, protective tariffs have disadvantages as well. They can backfire if countries whose trade is disadvantaged by the tariff impose tariffs of their own, resulting in a trade war. Some economic ideologies hold that tariffs are a harmful interference with the laws of the free market. They claim that it is actually disadvantageous for a country to artificially maintain an inefficient industry, and that it is better to allow it to collapse and to allow a new one to develop in its place. The opposition to all tariffs is called the free trade principle, and is a key policy of the World Trade Organization.