A wealth of new research and political developments around the country support the position that pre-K must be accessible to all children at age three as a core part of their right to a free public education. This brief offers the case for establishing a right to universal pre-K in three parts: (1) The rationale: A review of the evidence showing that pre-K can be successfully mounted on a large scale and documenting its educational, social, and economic benefits for children, the educational system, and society at large; (2) The definition of the constitutional right to universal pre-K that needs to be established as well as the essential elements of the educational opportunities that such a right would entail; and (3) The legal strategy: A national overview of the current state of the law on access to pre-K services as a constitutional right, based on an analysis of constitutions and legal decisions, and a review of state laws and policy documents. Building on these precedents, this brief suggests a legal strategy for establishing universal access to pre-K as a constitutional right. A sidebar presents such efforts by the state of New York. [Additional support was provided by Early Childhood Partners.]