Age-dependency ratios are a measure of the age structure of the population. They relate the number of individuals that are likely to be “dependent” on the support of others for their daily living – youths and the elderly – to the number of those individuals who are capable of providing such support. The key indicator of agedependency used below relates the number of individuals aged less than 20 and of those aged 65 and over to the population aged 20 to 64. Two other indicators are presented in this section: the youth-dependency ratio (for individuals aged less than 20) and the old-age-dependency ratio (for persons aged 65 and more), both calculated relative to the number of individuals aged 20 to 64. Taken together, these ratios provide information about the demographic shifts that have characterized OECD countries in the past and that are expected in the future.