Recent developments in linguistic theory, as well as the growing body of evidence from languages other than English, provide new opportunities for deeper explorations into how language is represented in the mind of learners. This collection of new empirical studies on the acquisition of Spanish morphosyntax by leading researchers in the field of language acquisition, specifically contributes to the characterization of the L1 / L2 connection in acquisition. Using L1 and L2 Spanish data from children and adults, the authors seek to address the central questions that have occupied developmental psycholinguists in the final decades of the previous century and that will no doubt continue engaging them into the present one.