Adult language acquisition is famously more variable and typically much less successful than child language acquisition. This means that some individuals experience much better success as language learners than others. To what extent can this variability be explained by individual differences in cognitive abilities? Furthermore, if the relevant cognitive abilities are known for a learner, can something be done to improve their learning outcomes? This talk discusses several threads of research at CASL investigating aptitude for language learning in adults. I'll give an overview of theoretical goals and practical applications that CASL is currently working on.