When fertility begins to decline from elevated levels, the population distribution by age changes. Initially, the reduction in fertility leads to an increase in the relative size of the population at working ages, creating a favourable age distribution that may help to accelerate economic growth per capita, resulting in a “demographic dividend”. Subsequently, this transformation will lead to an increasing concentration of the population at older ages, known as “population ageing”. Changes in the age distribution have major implications for labour markets, households, social protection, education and health care, and should be factored into strategies for implementing the 2030 Agenda for Sustainable Development. The Population Division monitors levels and trends in the population age distribution and analyses their socio-economic implications, including for the living arrangements of older persons. The Division produces World Population Ageing on a regular basis.