Although significant attention has been paid to promoting the importance of physical activity in children, adolescents, and adults, we do not currently understand how to promote sustained physical activity levels throughout the lifespan. We contend that previous research has failed to consider the dynamic and synergistic role that motor skill competence plays in the initiation, maintenance, or decline of physical activity and how this role might change across developmental time. In this article, we present a conceptual model hypothesizing the relationships among physical activity, motor skill competence, perceived motor skill competence, health-related physical fitness, and obesity. We contend that the development of motor skill competence is a primary underlying mechanism that promotes engagement in physical activity. (Contains 1 figure.)