Using a data-driven qualitative approach and drawing from language socialization and communities of practice theories, this dissertation study examines the second language (L2) identity-building strategies of 22 American learners of Russian who engaged in a six-week telecollaborative project with Russian native speakers in two genres of Internet-mediated communication: in one-on-one interactions with an assigned native Russian speaking keypal and in selected virtual communities populated predominantly by native Russian speakers. The investigation of L2 identity enactment in Internet-mediated environments was guided by three research questions pertaining to (1) the nature of the discourse Russian (L2) learners use in interactions with native speakers in two genres of online interactions, (2) the discursive manifestations of L2 learner and speaker identity performances in the learners' online discourse; and (3) the learners' perceptions of their online experiences in two genres of online interactions with native-speaking peers. The methods of critical discourse analysis and interpretative phenomenological analysis were employed to examine the Russian learners' online interactional discourse and offline metatalk regarding their online experiences in the two genres. The analysis of the Russian learners' discourse revealed the complex nature of discursive L2 identity enactment as they moved into and out of the frames of language learners to complete class assignments and negotiate their competent L2 speaker positions in conversations with Russian-speaking peers. The findings indicate that the two genres of online interaction evoked distinct participation patterns and interactional practices. In both genres, L2 identity enactment involved three dimensions: the macro-level of global identity categories, the locally assigned identity positionings (e.g., heritage speaker, multilingual speaker), and interactionally negotiated stances and temporary positions that evoked self- or other-initiated L2 learner/speaker identity performances. The author concludes that L2 identity, when enacted in Internet-mediated environments, represents a continuum of L2 learner-speaker performances that rely on the contextual factors of the online encounter, learners' global identity tokens, and the dynamics of power relations in native-nonnative speaker interaction. Performing an L2 identity online is construed as a critical experience of re-evaluating one's association with the target language and transformation into a new kind of socially oriented multilingual subject.