This study explores the writing of Wikipedia articles as a form of authentic writing for learners of English in Hong Kong. Adopting "Second Language Socialization and Language Learning & Identity" approaches to language learning inquiry, it responds to an identified shortage of research on computer-mediated language socialization. Focus is placed on the development of participant identities as valid writers of English texts for a perceived mass public. As part of Wikipedia writing praxis, writers are socialized to varying degrees into the community of Wikipedia. This study focuses on Hong Kong university students' reported experiences as legitimate peripheral participants, looking at the early stages of potential community membership. Ethnographic observations serve to provide a description of both the classroom and the Wikipedia site as dynamic social settings. Data sources include field notes, participant-generated written reflections, and transcripts of focus group interviews. Through these various channels it becomes clear that perception of a potentially vast reading public wields a subtle but important influence. Experiences with the Wikipedia community also play a role, motivating some participants to think deeply about their writing and prompting them to invest in writer identities online and in their local context.