Many scholars have highlighted the great variability of second language acquisition outcomes and, thus, the inconsistencies and inconclusiveness in the study abroad literature. These have called for longitudinal, case-based research that focuses on the students’ processes (rather than outcomes) and that showcases the heterogeneity of experiences in two ways: by pointing at students’ socialization abroad as a key aspect affecting outcome and by accounting for other interlinking factors that may affect the students’ different trajectories. From a discourse-analytic approach, this article presents a longitudinal, qualitative multiple-case study of the Erasmus experience of nine Catalan-Spanish undergraduate students in Italy, Denmark, and the United Kingdom. The focus will be on the reported linguistic impact of their sojourn abroad; how this is related to the social networks formed abroad; and the factors that shaped the participants’ socialization patterns and ultimately their second language learning and use trajectories.