This book collects some of the most significant articles by Adriana Belletti published over the last ten years or so, offering readers a useful tool to see the mutual enrichment between linguistic theory and experimental studies on (modes of) language acquisition through her work. The volume explores domains of theoretical morphosyntax in the generative tradition and theoretically guided studies on language acquisition. An introduction specific to this volume contextualizes these contributions within ongoing developments in the field. Part I presents studies inspired by the illuminating interchange between linguistic theory and experimentation in the domain of language acquisition, leading to the formulation of explicit research questions tested experimentally and guiding in the proper interpretation of the results. Part II offers refined, detailed theoretical analyses of domains in which peripheral positions in the clause structures are crucially involved to express discourse contents, in sometimes not standard ways during development. Demonstrating how refined linguistic analyses play a crucial role in interpreting the peculiar shape of developmental data, this book will be of interest to scholars in syntax, language acquisition, and theoretical linguistics.