This chapter examines the effects of foreign language anxiety (FLA). Research across diverse learning contexts has consistently shown that FLA negatively impacts foreign language (FL) learning in academic, cognitive, social, affective, and personal domains. Academically, FLA is associated with lower achievement and higher dropout rates. Cognitively, anxiety disrupts task performance by dividing attention between task-related and self-focused thoughts. Socially, anxious learners engage in less communication than their more relaxed peers. Affectively, FLA undermines self-confidence, motivation, and attitudes toward language learning. On a personal level, it can lead to severe emotional distress and even traumatic learning experiences. It is important to note that most of these findings are based on correlational studies, which do not establish causality. Future research would benefit from incorporating experimental designs to better understand the causal impact of FLA on language learning outcomes.