This article provides an analysis of the relationship between the Southern Common Market (Mercosur) and the European Union (EU) focusing on its purposes and functions, by exploring the literature on interregionalism through the perspectives of three distinct schools of thought: neorealism, neoliberal institutionalism and constructivism. Considering the functions theoretically fed by these theories behind interregional relations‐balancing, institution‐building and collective identity‐building‐, the paper attempts at providing a comprehensive understanding of the factors influencing the past and current purposes and functions of Mercosur‐EU relations and holds the potential to anticipate future trends. Our central argument underscores the enduring relevance of the setting of rules and norms and the focus on material gains in shaping the core of the relationship, particularly regarding the trade agreement, while the ideational function of sharing collective identity and values has experienced certain erosion. Nevertheless, increasingly crucial will be the geopolitical purpose, concerning balancing and counterbalancing external actors, given the current era of geopolitical upheaval where binary narratives fall short. We are not concerned with forecasting the future of the relationship as a whole; instead, we aim to analyse which functions will hold greater significance.