"International student security" refers to the international student's maintenance of a stable capacity for self-determining human agency. The article focuses on the role of English-language proficiency in the security of students from English as Foreign Language countries, drawing on evidence from a program of semistructured interviews with 200 international students. The interviews show that language proficiency is a pervasive factor in the human security of the international students in all domains inside and outside the classroom. There is a strong link between language proficiency and the capacity for active human agency. Both findings confirm prior research literature. The article concludes with implications for practice and for further research. (Contains 1 table.)