The twentieth century saw a revolution in longevity. Average life expectancy at birth has increased by 20 years since 1950. The remarkable demographic transition under way will result in the old and the young representing an equal share of the world's population by mid-century. In some developed countries, the number of older persons will be more than twice that of children by 2050. This transformation has profound consequences for everyone. While developed countries will face major resource challenges, developing countries face the challenge of simultaneous development and population ageing. International Day of Older Persons aims to raise awareness of the impact of population aging and the need to ensure that people everywhere are able to age with security and dignity and to continue to participate in their societies as citizens with full rights.