The present work examined the predictive role of phonological awareness and decoding accuracy in second language (L2) learning. Study 1 examined the role of native language (English) decoding accuracy in predicting second language (Spanish) learning in college-age adults. The study tested the hypothesis that the predictive relationship between native language (L1) decoding accuracy and second language learning is mediated by decoding accuracy in the second language. The results were in line with the hypothesis. Study 2 tested theoretical models of second language (English) reading comprehension among native Spanish speaking children. The model hypothesizing an indirect relationship between L2 phonological awareness and L2 reading comprehension, as mediated by decoding and vocabulary in the L2, was more parsimonious and consistent with the observed data than the alternative model. However, both models suggested that the two most important skills for reading comprehension in English (L2) are decoding accuracy and vocabulary knowledge.