This article is one of the first studies to use econometric techniques to examine the factors influencing proficiency of English as a foreign language. Specifically, this article aims to investigate, at cross-country level, the linguistic and nonlinguistic factors influencing the variation of proficiency in the use of English as a second language. As a proxy for English proficiency, we use the average Test of English as a Foreign Language (TOEFL) scores achieved by residents of a total of over 60 countries. The regression results suggest that linguistic factors such as historical affinity and similarity in word order between English and a given language have an influence on the proficiency in English achieved by people whose native language is not English. Among the nonlinguistic factors, expected years of schooling and degree of globalization have a positive relation with proficiency in English. These results seem robust, even when the computer-based TOEFL score is used in place of the paper-based TOEFL score and even when the overall score is replaced by the respective score in listening comprehension, structure and written expression, and reading comprehension.