Decision-makers have a professional and moral obligation to ensure that adolescents are involved in the development, implementation and monitoring of all relevant legislation, policies and services. Adolescents need to be included in developing the programmes affecting their lives, whether at school, in their communities or at national and international levels. This guide outlines the rationale for including children and adolescents in decision-making. It presents guidance on how participation with young people can be planned and executed to inform policy and practice developments and calls for policy-makers to prioritize both marginalized and seldom-heard adolescents and young children in decision-making.