This thesis examines the MERCOSUR agreement (Common Market of the Southern Cone), specifically the provision for a common external tariff and its impact on the economy of Uruguay. The thesis begins by examining the economic regionalism which gives rise to trade agreements such as MERCOSUR and investigates the trade mechanisms through which such regionalism is accomplished. The provisions and background of the MERCOSUR agreement are explored, as well as the economic conditions, current and historical, which exist in the participant countries. The work continues by exploring two possibilities for Uruguay: (1) to continue economic integration by entering a customs union scheduled to take effect on January 1995 or (2) to remain in a free trade zone with the other three countries (Argentina, Brazil and Paraguay). These two possibilities are analyzed using traditional and new theories of international trade. The study further examines foreign direct investment and technology in the context of Uruguayan participation in MERCOSUR or in a free trade zone. The study concludes that if Uruguay, due to its small size, could obtain the special treatment of a free trade zone, the costs of trade diversion would be reduced and Uruguayan welfare would increase.