For years, the unique health issues associated with adolescence have been little understood or, in some cases, ignored. But that has now changed. Adolescent health and development was made an integral part of the Global Strategy for Women’s, Children’s and Adolescents’ Health (2016–2030) (The Global Strategy) because, in the words of the United Nations Secretary-General, “[adolescents are] central to everything we want to achieve, and to the overall success of the 2030 Agenda”. Why “central”? Because investments in adolescent health bring a triple dividend of benefits for adolescents now, for their future adult lives, and for the next generation. Their health and well-being are engines of change in the drive to create healthier, more sustainable societies. In 2014, the WHO report Health for the World’s Adolescents showed that considerable gains from investments in maternal and child health programmes are at risk of being lost without corresponding investments in adolescent health. The latest data show that more than 3,000 adolescent die every day from largely preventable causes, and that many key risk factors for future adult disease start or are consolidated in adolescence. Adolescent mental health and well-being are often overlooked. This Guidance is a milestone for translating the Global Strategy into action. It provides a wealth of information to policy-makers, practitioners, researchers, educators, donors, and civil society organizations – including the most up to-date data on the major disease and injury burdens that affect adolescents. It supports the implementation of the Global Strategy by providing the comprehensive information that countries need to decide what to do for adolescent health, and how to do it. It builds on on-going efforts to ensure that adolescents can Survive, Thrive and are in a position to Transform the societies in which they live.