Publicly supported, high-quality preschool education is among the most successful and well-documented of education reforms. There is near-universal agreement that high-quality preschool programs more than pay for themselves in economic and social benefits. Program quality is absolutely critical. While no one factor can be considered determinative, some key program quality elements include: (1) Small class sizes and ratios--20 or fewer children, with two adults; (2) Well trained, adequately compensated and qualified teachers; (3) Strong links to social and health services; and (4) Attention to families' needs, including wrap-around child care. A number of other issues are frequently raised. Here's a summary of the key research: (1) Very Early Interventions; (2) Extended Day and Year; (3) Universal "versus" Targeted Enrollment; (4) Center-Based Programs; (5) Private "versus" Public Programs; (6) Head Start; and (7) Curriculum. This paper offers recommendations for policymakers. (Contains 20 notes and references.)