Following a proposal submitted by the Argentine Socialist Party, the Amsterdam (1904) and Stuttgart (1907) congresses of the Second International discussed the question of international migrations. The Argentine draft resolution sparked an international debate that went far beyond the local concerns that had originated the initial proposal. The 'migration question' proved to be a core concern that threaded together very important political problems for the International, for which socialist parties of different countries had divergent solutions, because the situations and contexts they faced at the local level were very different. As was the case with debates on militarism and colonialism, the migration question showed that, behind the principled positions and a practice of internationalist sociability, the Second International showed tensions that divided national parties. Drawing upon extensive secondary bibliography, socialist newspapers from different countries and archival materials of the Second International, this article presents some first conclusions on this important aspect of the international history of socialism, little explored in Spanish. It does so by reviewing the debates of the Amsterdam and, above all, the Stuttgart congresses, but also contextualizing them with the situation and the approaches of different national parties.