Book excerpt: In today’s digital era, increasing numbers of youth around the world learn English outside classrooms, frequently with the use of technology. This timely book brings together research and theory on the increasingly common phenomenon of Informal Digital Learning of English (IDLE) among students of all ages and across a wide range of contexts globally. By examining the positive impact of IDLE on students’ reading, writing, listening, and speaking abilities, as well as the unique challenges that result, Lee synthesizes research in one accessible and comprehensive volume in this rapidly developing domain. This book addresses key concepts, including Computer Assisted Language Learning, the impact on standardized assessment, and the role of classroom learning. Lee offers empirically tested activities, pedagogical recommendations, and lesson plans to engage ESL/EFL students. The research overview and practical offerings make this an ideal text for courses in TESOL on online education, language teaching online, digital learning, community and language, and applied linguistics.