The new call for a universal preschool system is prompting an important policy debate across California. How preschooling is expanded and improved with limited public resources depends on several key issues. The hopeful ideals of "preschool for all"--with children beginning school ready to learn--spark enthusiasm and broaden public will. But tough policy questions must be addressed by early educators, parents, and policy makers: (1) Should California build and run a "universal system" of preschool, or should public support be targeted on these children who reap the greatest benefits and families who face the highest barriers to access? In other words, who will benefit and who should pay? (2) Who should operate universal preschool--local "schools" or the current "mixed market" of providers, including nonprofit centers and licensed family child-care homes? (3) How can the quality of preschool be improved? Does raising the credential levels of teachers yield discernible gains for children? Would other policy options more cost-effectively boost quality and children's development? (4) How should preschool be structured for diverse families? Does clearer specification of learning standards and the formalization of instruction inside preschools benefit children? Does more regimented instruction imply a single language and with what effects on non-English speaking children? This review considers evidence on these pivotal questions from around the nation, applying these findings to current debates in California. An appendix delineates specific questions that county and state agencies might consider as they attempt to assess the effects of their preschool initiatives. (Contains 104 endnotes, 3 tables, and 2 figures.)