This volume is a comprehensive, state-of-the-science treatment of the acquisition of different Indo- and Non-Indo-European languages in different contexts (i.e., L1, L2, L3/Ln, bi/multilingual language, heritage languages, pathology and language impairment and sign language acquisition) conducted within the generative framework. It also encompasses the diversity of methodologies and issues that can be found with contemporary research in the field. The different chapters contain original research from several different angles and provide a basis for dialogue between researchers working on diverse projects with the aim to further our understanding of how languages are acquired and, at the same time, refine and propose new theoretical constructs, such as complexity of linguistic features as a relevant factor forming children’s, adult’s and bilingual’s acquisition of syntactic, morphological, lexical and phonological structures.