The decline in physical activity and the widespread adoption of a sedentary lifestyle among young people, along with their health consequences and social and economic impacts, are now well established. The Icaps study, "Intervention with Middle School Students Focused on Physical Activity and Sedentary Behavior," scientifically demonstrated, after four years of experimentation, that promoting regular physical activity helps prevent sedentary behavior and overweight issues among young people. Its effectiveness is based on the dynamic interactions between young people and their physical and social environments. This practical guide, the result of a collaboration between the Icaps team and the National Institute for Prevention and Health Education (INPES), aims to support school professionals, local authorities, associations, or government agencies in implementing initiatives to promote physical activity among children and adolescents, by providing them with an effective strategy to follow. Numerous approaches are suggested for developing Icaps-style projects to engage with young people and their social circles, as well as their environment, to encourage physical activity in all its forms, both in daily life and during leisure time.