This article is inspired by a recent call for the establishment of "alliances for inter- and transdisciplinarity" issued by Julie Thompson Klein (2021) in this journal. Previously, in 2016, "Issues in Interdisciplinary Studies" published a Special Section devoted to Latin American experiences in interdisciplinarity and transdisciplinarity. The concept of "regionalism" was elaborated as a means to orient collaborative practices based on mutual learning and cooperation. Using this concept as an inspiration, this article explores the works of a network of Latin American researchers and practitioners called "Nodo de Estudios sobre Interdisciplina y Transdisciplina" (Nodo ESIT). The aim of this collective, created in 2018, is to promote, connect, and strengthen inter- and transdisciplinary teaching and research in different countries within the region. The Nodo ESIT offers a shared virtual space for exchange and collaboration among societal and scientific actors from different fields (i.e., academia, social organizations, decision makers, and the private sector). It represents seven countries in Latin America, and integrates participants from some European countries, who are working in the region. Drawing from the concept of regionalism and expanding Klein's (2021) description of the similarities and differences among five international organizations, we elaborate on our network's opportunities and the challenges it has faced in the Latin American context. Two questions guide this work: (1) How can inter- and transdisciplinarity be supported and enhanced in marginalized contexts? and (2) What are the best practices already implemented to foster inter- and transdisciplinarity in Latin America? We present the Nodo ESIT as an exemplary case of regionalism for inter- and transdisciplinarity in Latin America. We conclude by identifying three lessons learned and strengths achieved from this initiative thanks to a special constellation of actors, contexts, and actions.