We are delighted to have this volume included in the series Handbooks of Applied Linguistics. As a field, applied linguistics investigates language-related real-world is-sues – particularly those concerning language use, language acquisition and learn-ing, and language teaching – and works towards describing and explaining these processes and suggesting ways to enhance them. It approaches these issues from an interdisciplinary perspective, drawing not only on linguistics but also on neighbour-ing disciplines such as education, psychology, and sociology. Each of the earlier vol-umes in the handbook series presents an overview of their chosen field, identifies the most important traditions, their research findings, and gaps in current research, and provides perspectives for future research directions. So too does this volume. Couched in one of the main branches of applied linguistics research – bilin-gualism (which in our understanding includes notions of multilingualism and plurilingualism) – this volume focuses on social and affective factors in home lan-guage maintenance and development. Bilingualism research has extensively ex-plored linguistic and psycholinguistic perspectives, and educational practices and outcomes. Yet the social and affective perspectives that impact on home lan-guage maintenance and development have remained somewhat less researched, a gap that is addressed in this handbook. This is the first volume that brings together the different strands of research into social and affective factors of home language maintenance and development. Contributors from around the world present a rich harvest of research paradigms and perspectives, providing a comprehensive and constructive overview of the state-of-the-art in this flourishing field.