In communities all over the country, afterschool programs play an important role in keeping children and youth safe, providing them with important learning opportunities, and helping them become successful adults. Federal, state, local, and private investments in afterschool programs have grown in recent years due both to widespread public support and a better understanding of the crucial role such programs play in serving children and youth and the communities in which they live. Afterschool programs come in many different shapes and sizes, from tutoring to drop-in sports leagues to more comprehensive programs that provide an array of activities for children as well as their families. Positive youth development, prevention, child care, education, skills development, mentoring?whatever the program approach, a growing body of evidence points to the important role quality afterschool programs play in helping children succeed both academically and socially. Despite the growth in attention and funding for afterschool programs, many questions remain about availability and accessibility. As policymakers consider funding for afterschool programs, they often want to know more about the current need for these services?especially among low-income families. Among the questions policymakers ask are: What programs are currently out there? How many children are being served? How many children would like to be in afterschool programs but for one reason or another are not? What resources currently support existing programs, and are they sufficient? This tool draws upon those experiences to outline concrete steps in the process of estimating supply and demand. It provides examples of states and communities that have undertaken this task, outlines a five-step process for planning and collecting data, and offers guidance and lessons learned from the field.