This paper examines the patterns of language choice and the construction of L2 learning opportunities in foreign language learners' social networks by focusing on how these patterns and opportunities are socially structured in a Japanese language learner's natural interactions. It is based on a range of data, including a script of on-line chat occurring in natural environments as well interview data. Drawing on Cummins' (1996) concept of interpersonal space, the findings indicate that there were a number of social and contextual factors that seemed to affect the learner's language choice and L2 learning opportunities in complex ways. Most of these factors appeared to be related to the learner's and/or his network interactants' identity as an adequate L2 user and their perception of each other's L2 proficiency and/or role. This paper provides insights into how to create environments that promote the learners' opportunities for L2 use and learning.