The purpose of this study is to improve our understanding of the determinants of and effects on young children's development of multiple, concurrent arrangements. Using data from the Early Childhood Longitudinal Study-Birth Cohort, this study examines families' selection into multiple arrangements, including the role of publicly-subsidized child care programs; estimates the associations between multiple arrangements and children's cognitive and socio-emotional development; and examines whether these relationships are moderated by child and family characteristics and the timing of multiple arrangements.