The articles in this special issue provide a complex picture of acquisition in bilinguals in which the factors that contribute to patterns of performance in bilingual children's two languages are myriad and diverse. The processes and contours of development in bilingual children are influenced, not only by the quantity, quality, and contexts of input, but by whether the child hears monolingual or bilingual speech, who is the source of that speech, the proportion of speakers of the heritage language in the community, the child's birth order in the family, the family's SES, the timing and the child's stage of development, profile effects in performance, and characteristics of the languages being learned. One constant across the research is the finding that the majority language fairs well in development, while the minority language is threatened. The insights gained are relevant to future work on bilingual children, whether of a theoretical or applied focus.