During the past three decades, extensive literature has accumulated on the early years of life for children. Research findings unequivocally agree that these years are a critical period of intense learning for children which provides the foundation for later academic and social success. This review explores the literature on the complex relationship between developmental outcomes and attendance at early childhood education and care programs. The article reviews Australian and international literature to evaluate the impact of both the quality and quantity of early childhood education and care (ECEC), the impact for different age groups, and which groups of children benefit most. The Australian early childhood education and care policy context is also described. [Additional funding for this report was provided by the Australian Government Department of Social Services.]