This dissertation consists of three theoretical papers that investigate how trade and tariffs redistribute income and welfare between countries and within countries. In the first paper, we set a perfect competition model of trade in intermediate (tasks) and final goods. Trade in intermediate goods will create income redistribution within a developed country and across workers whose jobs are of a different nature. In the second paper, we set a monopolistic competition model of trade in product varieties. Tariffs and mutual trade liberalization will modify the pattern of trade in product varieties thereby causing welfare redistribution between countries of a similar development level. Finally, we set model of trade in final goods and intermediate goods in which the government from a developed country will promote domestic monopolies by imposing tariffs. The promotion of domestic monopolies will shift foreign rents and then redistribute income across countries with different development levels