Language is the key interface between our social and cognitive worlds. As a social tool, it is the means by which human interactions occur, social position is determined, and educational opportunities are defined; as a cognitive instrument, it provides access to concepts and meanings, the logical system for problem solving, and creates the organizational basis for knowledge. It is not an accident that a significant portion of all developmental research is addressed to issues of language acquisition and language performance, that the primary focus of school curricula in the early years is on the language arts, and that an ongoing concern of parents is their children's language acquisition. Language has consequence. However, language acquisition occurs in a context, and differing environments are bound to influence the way language is learned and used by young children. Children growing up in bilingual environments will have different experiences than those who encounter only one language, and these differences may have a profound impact on children's social, cognitive, and linguistic development. Understanding how these linguistic environments affect children's development requires an examination of the interactions between the social and cognitive dimensions of development in different learning environments.