Recent years have seen a substantial growth in research on the economics of pre-K. This paper reviews this research. The review contains: a summary of what is known about the costs and benefits of pre-K; a report on newly emerging research and evidence; and a catalog of important unanswered questions. The review draws several conclusions with implications for future research. First, state level evaluations are often of little value: they “almost never attempt to address fundamental questions regarding what types of pre-kindergarten services work best and under what conditions of implementation” (Gilliam and Zigler, 2004). Second, it is not just at-risk children who might benefit from pre-K, even as the extent of the benefits to children from all socio-economic strata is not precisely known. Third, thus far, research has not directly compared pre-K with educational policies that may actually be implemented, such as increased pay for teachers or reduced class size. Finally, economic and demographic changes are likely to reinforce the need for investments in pre-K and other early childhood programs; the full extent of this remains to be determined.