Accurate, consistent and timely data on global trends in population age structure are critical for assessing current and future needs with respect to population ageing and for setting policy priorities to promote the well-being of the growing number and share of older persons in the population. This publication summarizes the trends in population ageing drawn from the latest United Nations estimates and projections of population by age and sex of 233 countries or areas, as published in World Population Prospects: the 2015 Revision. The report focuses in particular on the period from 2015 to 2030, the implementation period identified for the 2030 Agenda for Sustainable Development, and discusses some implications of trends in the number and share of older persons for development planning, including with respect to poverty eradication and economic growth, social protection, and the health and well-being of older persons.