'Grit' has been identified as an important predictor of success in a number of academic and non-academic domains (Duckworth, A. L., C. Peterson, M. D. Matthews, and D. R. Kelly. 2007. "Grit: Perseverance and Passion for Long-Term Goals." "Journal of Personality and Social Psychology" 92: 1087-1101. doi:10.1037/0022-3514.92.6.1087). The present study responds to calls to examine language-specific (L2) grit. We investigated the factor structure of the L2-Grit Scale (Teimouri, Y., L. Plonsky, and F. Tabandeh. in press. "L2 Grit: Passion and Perseverance for Second-Language Learning." "Language Teaching Research," 1-26. doi:10.1177/1362168820921895) and examined the predictive validity of grit and three other individual differences in relation to English proficiency among second and foreign language learners from different countries. Factor analysis revealed a two-dimensional structure of the L2-Grit Scale. However, the correlation between the factors was stronger in the EFL than in the ESL sample. Moreover, the L2 grit subscales had differential predictive validity: Perseverance of Effort was a significant positive predictor of proficiency in the EFL context, while Consistency of Interest was a significant negative predictor in the ESL context. This study represents one of the first inquiries into L2 grit and how it relates to the learning context in particular.