Book excerpt: The study of informal involvement with additional languages has recently emerged as a dynamic research field in SLA. With the rapid development and spread of internet-based technologies, contact with foreign languages outside the classroom has become commonplace. While this can take multiple forms, online contents are a major driving force because they present learners with unprecedented opportunities for exposure to and use of target languages regardless of their physical location. Research from diverse geographical, educational and socio-economic contexts bring a rich variety of perspectives to this book. It explores these phenomena via a range of theoretical frameworks and methodological approaches, focusing particularly on individual differences and language development. The volume proposes that teachers in formal learning settings should seek to support and facilitate the development of these identities and practices, and it indicates means they can adopt to best do so.