Foreign language anxiety (FLA) has been widely recognized as a prevalent emotional response in language classrooms with significant negative effects on learning. This chapter introduces the sustained scholarly interest in FLA and explains the rationale for this volume. It also outlines the book’s main topics, including FLA measurement, nonverbal indicators, sources and effects of anxiety, associated factors, intervention strategies, and recent developments. Research on skill-specific anxieties and heritage language learner anxiety is also addressed, though not as separate chapters.