The twenty-first century presents three main trends related to maritime spaces: firstly, the growing importance of the oceans in economic globalisation, global environmental agenda, and international politics; secondly, the increasing tensions arising from the demarcation of the state’s maritime borders, regulated by the United Nations Convention on the Law of the Sea (UNCLOS); and thirdly, since 2017, the official return of competition between the great powers, announced in the US National Security Strategy, published in that year. While the great powersGreat powers compete, contributing to generating more tensions and conflict in the maritime environment, they also cooperate for the maintenance of the globalised maritime system. The South Atlantic is part of this system and is affected by the dynamics of global geopolitics. For Brazil, the largest South Atlantic country, the ocean plays an important economic, political, and strategic role. In this context, this chapter seeks to answer the following question: What are the opportunities and challenges that Brazil faces in the South Atlantic due to the competition between China and the United States in the region? The chapter contains three parts. The first part deals with the importance of the geopolitics of the oceans. The second part analyses the security situation in the South Atlantic and the strategies used by China and the United States in the region. Then, the focus turns to the opportunities and challenges Brazil faces in search of its geopolitical objectives in the South Atlantic amid the competition between China and the United States. The research was carried out using documentary analysis and data collection from primary and, occasionally, secondary documentary sources.