This doctoral dissertation is divided in three chapters that advance our understanding of the relationship between population ageing, productivity, and social protection. The study starts at the root of these issues, by reviewing the definition of ageing. According to the World Health Organisation’s (2015) authoritative report, ageing at the individual level is related to social and biological characteristics that negatively affect a person’s capacity to pursue whatever they value, including their participation in the labour force. Across time, these characteristics are not necessarily linked to an individual’s age. However, the most common indicator of aggregate population ageing, the old-age dependency ratio (OADR), is exclusively based on the population age structure. Relying on such age-based (also called chronological) measures can create a bias in the way we understand the consequences of population ageing…