With a focus on childhood and adolescence, this chapter seeks to understand how people come to act responsibly on behalf of the environment. It begins with a brief overview of selected theories related to the development of agency and the motivation to act as a framework for research reviews in three areas of young people’s experience: informal play and exploration in nature; environmental education programs in schools and in the field; and wilderness experience programs. The chapter compares research results in these areas with the goal of understanding the types of experiences that prepare young people to take action for the environment, considers how these results correspond with processes that would be predicted by developmental theory, and distills recommendations for the design of school-based programs, wilderness adventure programming, and the design of communities that facilitate free access to nature. Directions for future research are suggested.