Tariff barriers today are small on average, suggesting only limited welfare gains from their removal. This column argues, however, that the current generation of standard trade models have missed an important source of gains from trade by neglecting the more complex case of a world with production linkages and multiple sectors. Under monopolistic competition, the effects of firm entry may be so powerful, that optimal tariffs are not positive but negative. Even the removal of small positive tariffs could thus produce significant welfare gains.
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