This chapter examines key factors associated with foreign language anxiety (FLA). Decades of research have shown that FLA is a multifaceted phenomenon that interacts with numerous variables throughout the foreign language (FL) learning process. These variables are categorized into two broad groups: categorical background variables and continuous (quantitative) variables. Commonly studied background variables include gender, academic year, language proficiency level, heritage learner status, course requirement status, ethnic background, study-abroad experience, and perceived peer standing. Quantitative variables frequently explored include learner-internal factors (e.g., age, aptitude, self-perceptions, achievement, personality traits, and affective variables), language-related factors, and teacher/classroom-specific variables. While findings regarding background variables have been mixed, research on quantitative variables has produced more consistent patterns. To date, most empirical studies in this area have employed a cross-sectional quantitative design, using statistical procedures such as descriptive analysis, independent and paired t-tests, ANOVA, correlation analysis, and multiple regression.