The research literature on outdoor recreation as it relates to human health is vast and growing. To help policymakers take new and emerging findings into account when designing recreation and park services and initiatives for the 21st century, this paper summarizes the salient issues and identifies research gaps. It considers how being outside in natural surroundings may improve health and how outdoor physical activities benefit participants. Particular attention is given to children’s health problems that can be mitigated through outdoor play, sports, and nature study. The paper describes approaches to measuring physical activity and recent trends in park visitation and outdoor activity participation. It looks at variables that affect participation in outdoor activities and considers the projected demographic changes that will affect policymaking in this arena. The findings of this literature review point to potential new directions for outdoor recreation policy, as well as new policy questions to be explored.