This is the first book on the acquisition of Spanish that provides a state-of-the-art comprehensive overview of Spanish morphosyntactic development in monolingual and bilingual situations. Its content is organized around key grammatical themes that form the empirical base of research in generative grammar: nominal and verbal inflectional morphology, subject and object pronouns, complex structures involving movement (topicalizations, questions, relative clauses), and aspects of verb meaning that have consequences for syntax. The book argues that Universal Grammar constrains all instances of language acquisition and that there is a fundamental continuity between monolingual, bilingual, child and adult early grammatical systems. While stressing their similarities with respect to linguistic representations and processes, the book also considers important differences between these three acquisition situations with respect to the outcome of acquisition. It is also shown that many linguistic properties of Spanish are acquired earlier than in English and other languages. This book is a must read for those interested in the acquisition of Spanish from different theoretical perspectives as well as those working on the acquisition of other languages in different contexts.