**Reference for chapter** Morgan-Short, K., Hamrick, P., & Ullman, M. T. (in press). Declarative and procedural memory as predictors of second language development. In S. Li, P. Hiver, & M. Papi (Eds.), The Routledge handbook of second language acquisition and individual differences. Routledge. **Abstract** We present a systematic review of research relevant to the question of whether individual differences in declarative or procedural memory predict second language (L2) abilities. We identified 33 studies that examined associations between a) aspects of learning abilities in declarative or procedural memory and b) aspects of L2, including lexicon, phonology, morphophonology, morphosyntax, and syntax, as well as other language abilities. The evidence suggests that learning abilities in both memory systems account for individual variability across various aspects of L2. The particular associations observed are largely predicted by our independent understanding of the two memory systems, that is, by the declarative/procedural model. Overall, the pattern of findings indicates that declarative and procedural memory contribute substantially to individual differences in L2. We discuss practical implications for L2 learning and pedagogy, highlight areas for future research, and suggest specific methodological approaches than can be employed to further our understanding of the contributions of declarative and procedural memory to L2 development.