This paper examines the contribution of the World Health Organization to the field of adolescent sexual and reproductive health (ASRH) from the early 1980s to the present. It is based on published documents and on the experiences of WHO staff members who have been part of much of this journey. It recalls the responses of the organization to the (then) new HIV/AIDS pandemic and to the first calls for a global public health response to early pregnancy. It also highlights selected milestones in the organization's work in the ASRH field over the last 25 years. It concludes with an analysis of where the ASRH field stands today and what the organization is doing to strengthen the epidemiologic and evidence base for action, to build consensus and coordination, and most importantly to support country level action, in cooperation with organizations within and outside the United Nations system. In defining its niche in a rapidly evolving and increasingly crowded field, the WHO's mission on ASRH is to contribute to a world in which the importance of ensuring the sexual and reproductive health of adolescents is understood, accepted, and acted upon by adolescents themselves, by their families and communities, by the workforces of different sectors, by civil society bodies, and by leaders and decision makers.