This dissertation analyzes the Brazilian participation in the G-20, a coalition of developing countries created by Brazil and India during the World Trade Organization (WTO) Ministerial Conference held in Cancún, Mexico, in 2003. The goal of the coalition was advancing an agenda of agricultural liberalization in the Doha Round. At the time, trade policy experts were skeptical as to the chances of survival of the coalition, due to the fact that it brought together countries with divergent commercial interests in agriculture. In spite of this, the G-20 established itself as a sine qua non member of the negotiations and changed the decisionmaking process of the WTO, with the inclusion of Brazil and India in the core of the negotiations together with the United States and the European Union. However, this increase in influence has not translated into a conclusion of the Doha Round, of extreme interest for Brazil. We argue that this difficulty is related to the fact that the G-20 is a coalition with low internal coherence and that its structural characteristics constrain its negotiating strategies, making it difficult for the coalition to adopt a distributive strategy that increases the probability that the negotiation is concluded successfully. Brazil played an important role paying the collective action costs in order to maintain the cohesion of the coalition, even when this meant going against its own commercial interests. However, this attitude had its limits, as was made apparent during the WTO meeting in Geneva, in July 2008, when Brazil decided to defend its own interests in detriment of cooperating with the members of the G-20.