What motivates adolescents to participate in organized activities-those the authors term primary supports-and what sustains their involvement? The authors begin this article by proposing conceptualizations of participation, and move on to examine a number of variables linked in the research with participation levels. These variables are demographic characteristics, school achievement, educational history (of both youth and parents), parents' attitudes and beliefs, individual psychology, peers, and program structure. The authors explore social psychological models of youth participation, a sequential specificity approach, and the field of "leisure constraints" in an attempt to further understand participation. In the final section, they distill lessons learned from the literature on this subject.