This study investigated second language metalinguistic knowledge, or explicit knowledge about the second language, in English-speaking university-level learners of German and Spanish. The status of metalinguistic knowledge in relation to the individual difference variables of language-learning aptitude, working memory for language, and participants' language-learning history was identified. Language-learning experience in formal settings was found to be the strongest predictor for levels of metalinguistic knowledge attained by the participants. Moreover, it was found that despite a significant relationship with language-learning aptitude, metalinguistic knowledge is separable and distinct from both aptitude and working memory. In conclusion, suggestions for further research are put forward.