This chapter reviews the role of theories in the evolution and transformations of regionalism in Latin America. The demand for developing regional cooperation and integration mechanisms in Latin America in the late 1950s follows the premises of the European integration process. Over time, the Latin American process found some obstacles to advancing the regional agenda, paving the way for more flexible cooperation formulas and waves of regionalism. While explanations and theorization were primarily Eurocentric, the peculiarities of regionalization projects in Latin America have demanded a supply of innovative theoretical and conceptual debates regarding Latin American regionalization. The result of the transfer of Eurocentric theories and concepts was ambivalent. On the one hand, it stimulated theory-driven research on Latin American regionalism; on the other hand, Eurocentric approaches produced misinterpretations and ended up in dead ends, which ultimately led to the emancipation and differentiation of Latin American regionalism research from Eurocentric analytical approaches and theories, without, however, completely abandoning the reference to research on the EU.