This book aims to explore the implications for language acquisition theory of a case study in bilingual acquisition. The subject is a child who acquired English and Spanish from birth, and the analysis focuses on various aspects of her language development during the second year of her life. The authors analyse aspects of the development of her sound system, her vocabulary, her early syntax, and her ability to choose languages appropriately. They discuss issues such as: What are the important cues used by children when acquiring contrasts in their sound systems? How are the sound systems from two languages differentiated by children? Is it possible for children to have two words meaning the same thing in their early vocabulary? Is it possible to identify two linguistic systems in the early two-word utterances of bilinguals? How early are children able to make appropriate language choices? This study is unusual in that it focuses on a bilingual child under the age of two. The methodology of data collection is fully discussed, and the book includes a extensive lists of the child's words in English and Spanish, as well as her two-word utterances.