We are pleased to present this collection of profiles of professional development initiatives that are hosted by organizations promoting the healthy development of children and youth during the out-of-school time (OST) hours. These profiles were organized as part of a Commissioned Analysis of the implementation of the National AfterSchool Association's Physical Activity Standards which was funded by the Active Living Research Program of the Robert Wood Johnson Foundation (RWJ #70583). The National AfterSchool Association adopted the Healthy Eating and Physical Activity Standards developed by the Healthy Out-of-School Time Coalition (HOST) in 2011. The Physical Activity Guidelines for Americans Midcourse Report identified Community and Out-of-School Time Program settings as showing limited evidence about specific intervention strategies to increase physical activity among children and youth, and noted that these settings should be highlighted as priority areas for additional research. There is among OST service providers, intermediaries, and advocates, a substantial interest in, and organization around, promoting physical activity in OST settings, and equipping program leaders and staff with the necessary skills and strategies to work effectively on raising children and youth's physical activity participation. A number of promising professional development models do exist. These models offer insight and guidance towards training program leaders and front line staff in the delivery of high quality physical activity experiences during the OST hours. It is our hope that this collection of profiles is responsive to some of the gaps identified in the Midcourse Report and informs providers, funders, school administrators, and policy makers about promising approaches to increasing physical activity for children and youth participating in OST programs. OST programs can be a significant contributor to childhood wellness and chronic disease reduction and we place great value on this "practice-based evidence" emanating from the field. (author abstract)