As globalization spreads, English has become a lingua franca. Emerging technologies (e.g., Artificial Intelligence) now make learning English more accessible, affordable, and tailored to each learner. Social media and digital platforms immerse users in English, offering interactive, personalized, and engaging experiences that fuel Informal Digital Learning of English (IDLE). Research spanning more than ten regions has found that IDLE brings a wide range of benefits, including greater motivation, higher academic achievement, and stronger speaking skills. Today, IDLE is being woven into schools and local communities through partnerships among teachers, NGOs, and industry leaders. This volume seeks to (a) showcase the latest research on IDLE, (b) highlight examples of IDLE in educational and community settings, and (c) chart future pathways for practice, research, and collaboration.