In recent years, analysts have argued that the United States' influence in Latin America is waning; others add that Washington is being replaced by actors from the region and beyond. However, even when Washington was at the height of its power, Latin American leaders were influential in shaping hemispheric relations, sometimes centrally—albeit in ways that have seldom been recognized. This dissertation examines Latin American foreign policy vis-à-vis the United States, asking whether and how Latin American leaders are able to influence US policies that affect their interests. Building on the IR literature on small or weak states, it argues that weaker-state leaders are indeed able to exercise substantial influence in international relations, but they do so differently than great powers. Instead of employing traditional power capabilities, they must rely on a combination of opportunities, allies, and ideas. The dissertation employs multinational archival research and interviews to analyze US-Latin American relations in four historical case studies—Brazil's Operação Pan-Americana in the late 1950s, the negotiation of the Panama Canal Treaties in the 1970s, the emergence of the North American Free Trade Agreement in the early 1990s, and the creation of Plan Colombia in 1998-2000–to examine how Latin American leaders define and pursue their interests when facing the world's most powerful country.