The current study examined second language (L2) learners' social networks during study abroad and how they changed over time. Participants were 29 British undergraduates majoring in French who were spending an academic year abroad in France. Social network data were collected three times during study abroad (beginning, middle, and end of a nine-month stay) using the Social Networks Questionnaire. Results showed that large proportions of learners' social networks included L1-using contacts, with little change over time. Analysis of social networks according to social context indicated that work/university and organised free time contexts appeared to favour L2 use, whereas virtual contexts (e.g. Facebook, Skype) appeared to favour L1 use. Correlations between aspects of learners' social networks and language development (lexical complexity scores in oral interviews) indicated complex and changing relationships over time, indicating that frequent amounts of L2 use during study abroad were associated with high lexical complexity scores.