This book explores the relationship between online second language (L2) communicative activities and formal language learning. It provides empirical evidence of the scale of L2 English use online, investigating the forms most commonly used, the activities likely to cause discomfort and the challenges experienced by users, and takes a critical approach to the nature of language online beyond the paradigms of 'written' versus 'spoken'. The author explores the possibilities for language teaching practices that engage with and integrate learners' L2 English online use, not only to support it but to use it as input for classroom learning and to enhance and exploit its incidental learning outcomes. This book will be of interest to postgraduate students and researchers interested in computer-mediated communication, online discourse and Activity Theory, while language teachers will find the practical ideas for lesson content invaluable as they strive to create a successful language learning community.