Three states (Georgia, Oklahoma and Florida) recently introduced Universal Pre- Kindergarten (Universal Pre-K) programs offering free preschool to all age-eligible children, and policy makers in many other states are promoting similar policies. How do such policies affect the participation of children in preschool programs (or do they merely substitute for preschool offered by the market)? Does the implicit child care subsidy afforded by Universal Pre-K change maternal labor supply? I present a model that includes preferences for child quality and shows the directions of change in preschool enrollment and maternal labor supply in response to Universal Pre-K programs are theoretically ambiguous. Using restricted-access data from the Census, together with year and birthday based eligibility cutoffs, I employ a regression discontinuity framework to estimate the effects of Universal Pre-K availability. Universal Pre-K availability increases preschool enrollment by 12 to 15 percent, with the largest effect on children of women with less than a Bachelor’s Degree. Universal Pre-K availability has little effect on the labor supply of most women. However, women residing in rural areas in Georgia increase their children’s preschool enrollment and their own employment by 22 and 20 percent, respectively, when Universal Pre-K is available.