Most general theories of language acquisition are based on studies of children who acquire one language. A general theory of language acquisition must ultimately accommodate the facts about children who acquire two languages simultaneously during infancy. This chapter reviews current research in three domains of bilingual acquisition: pragmatic features of bilingual code-mixing, grammatical constraints on child bilingual code-mixing, and bilingual syntactic development. It examines the implications of findings from these domains for our understanding of the limits of the mental faculty to acquire language. Findings indicate that infants possess the requisite neuro-cognitive capacity to differentially represent and use two languages simultaneously from the one-word stage onward, and probably earlier. Detailed analyses of the syntactic organization of bilingual child language indicates, moreover, that it conforms to the target systems and, thus, resembles that of children acquiring the same languages monolingually, for the most part. At the same time, bilingual children acquire the distinctive capacity to coordinate their two languages in grammatically constrained ways and in conformity with the target grammars during online production. In short, current evidence attests to the bilingual capacity of the human mind and refutes earlier conceptualizations which viewed bilingualism and bilingual acquisition as burdensome and potentially disruptive to development.