Since the birth of Brazilian geopolitics in the early 1930s, the South Atlantic has been of concern to state interests and objectives, particularly in the fields of security and economics. Strategic thinking in relation to the South Atlantic changes in response to international developments, as well as national regimes and governments. This chapter explores the South Atlantic in Brazilian geopolitics from a historical perspective. It aims to better understand how the South Atlantic has been portrayed within Brazilian geopolitics and how this shapes government action. It focuses on the context of Brazilian geopolitical thinking over time, which had been interlinked to, or constructed in response to, specific situations. The main research question is: how has geopolitical thinking been incorporated into Brazilian security and defence documents and what are the resulting foreign and security policy practices? Drawing on official documents and secondary sources, the chapter identifies the security issues underpinning Brazil’s vision of this geographical area. As well as outlining the importance of the South Atlantic in Brazilian foreign and security agendas, the chapter examines when, how, and why the most relevant changes have occurred in relation to different governments and alterations in the international system.