This text sets high standards for rigor and scientific approach to the study of bilingualism and provides insights regarding the critical issues of theory and practice, including the interdependence of linguistic knowledge in bilinguals, the role of socioeconomic status, the effect of different language usage patterns in the home, and the role of schooling by single-language immersion as opposed to systematic training in both home and target languages. The rich landscape of outcomes reported in the volume should provide a frame for interpretation and understanding of effects of bilingualism for years to come.