The synthetic (virtual) world Second Life can be defined as a social networking environment for it allows users to network informally by initiating relationships with other users, often strangers with whom they share no previous offline connection. Users can also connect with other users with whom they have previously established offline relationships. In the synthetic world, networking can occur by interacting, and later friending, other users whose avatars are proxemically close to a user inworld. This is facilitated by the feature of the synthetic world which allows any interaction between users in the public audio or textchat channels to be heard / read by other nearby users. Users can also initiate relationships through similar interest groups and choose to create a public profile, albeit relating this profile to that of their avatar or their physical world (first world) identity. Users who friend each other can view the newsfeed and interest groups as well as the list of connections of one another, and can navigate the latter. The development of social networking environments allows users to construct online personae / identities which may differ from their first world identities (Turkle, 2011). The environments offer new ways of communicating both verbally and nonverbally which imply new ways of being, of showing and negotiating identities (Nagy, 2010). As fully anonymous social networking environments, synthetic worlds offer specific possibilities for identity construction and new ways of interacting because users are represented in the environment by an avatar through which they communicate. In the language-learning (L2) domain, interest is emerging in this type of environment. Research suggests that synthetic worlds may reduce student apprehension concerning interacting in a second language (Schweinhorst, 2002) and increase the students' sense of presence and community (Nowak and Biocca, 2004). However, the questions of whether and how language learners use avatars to develop an identity, the impact of avatar use on participation and interaction in a L2 remain largely unexplored. In this chapter, we explore the above questions through the data analysis from an experiment designed around a course in Second Life which formed part of the European project ARCHI21 . For this course, a Content and Language Integrated Learning (CLIL) approach was chosen for students of Architecture whose foreign languages (L2) were French (FFL) or English (EFL). We explore how these students developed their online identities and how these identities were forged through avatar appearance and the use of nonverbal acts, including gestures. We examine how these identities impacted interaction. Firstly, how changing avatar appearance influenced how students addressed each other inworld and their level of verbal participation in L2 interaction. Secondly, whether constructing an identity partially through nonverbal communication acts in this social networking environment may have created opportunities for increased L2 verbal participation. In our study, no instructions were given to the students regarding avatar appearance. The research questions presented here were formulated after remarking upon how students changed their avatar appearance and used nonverbal communication during the course. Our study focuses on the L2 interaction during open-ended activities rather than question-answer exchanges which may be more typical of a non-CLIL learning context.