This chapter examines the sources of foreign language anxiety (FLA), a pervasive phenomenon known to negatively affect language learning outcomes. Given its prevalence and detrimental impact, understanding the causes of FLA is of central concern to language educators seeking to alleviate learners’ discomfort in the foreign language (FL) classroom. Drawing on an extensive review of the literature, this chapter proposes a four-dimensional model of FLA sources, encompassing the classroom environment, learner characteristics, the target language, and the FL learning process itself. The chapter also highlights the dominant role of qualitative research in exploring FLA sources, with particular emphasis on the grounded theory study by Yan and Horwitz. Finally, pedagogical implications are discussed to inform instructional practices aimed at reducing FLA and fostering more supportive language learning environments.