The movement to establish public prekindergarten for all young children in the United States has steadily accelerated. Forty states now provide some form of classroom-based preschool services to at least some groups of children, whereas in the 1960s half the states did not even have universal kindergarten and just seven had limited programs for preschoolers (Gilliam & Marchesseault, 2005; Mitchell, 2001). Today there are throngs of advocates for universal preschool, including many outside the ranks of expected supporters like parents and early childhood educators. Surveys and public opinion polls repeatedly show that the majority of the public approves of state funding for prekindergarten programs and believes these should be available to everyone. As described in Chapter 1, private philanthropic foundations have mounted a national mission to promote universal preschool. Economists and members of the business community, whose opinions generally carry great weight among policy makers, have identified preschool as necessary to building a skilled and productive work force in coming generations. The time is right to capitalize on this momentum, to put our accumulated research on the benefits and cost-effectiveness of early education to use, and to urge all states to adopt or expand prekindergarten services. But this is also the critical time to guide the construction of these programs so they are of high enough quality to achieve the expectations being placed in them.