The relationship between ageing and skills is becoming an important policy issue, not least in the context of population ageing. Data from the Programme for the International Assessment of Adult Competencies (PIAAC) will potentially add considerably to the understanding of the relationship between ageing and foundation skills. In particular, the fact that data from the 1994-1998 International Adult Literacy Survey (IALS) and the 2003-2007 Adult Literacy and Lifeskills Survey (ALL) will be linked with PIAAC offers a unique opportunity to examine trends over time at the cohort level for a wide range of countries. Specifically, repeated measures will enable an analysis of whether there is skill gain and skill loss over the lifespan of cohorts and overtime between cohorts. This is especially important because age-skill profiles observed on the basis of a single cross-section are difficult to interpret. With this as a backdrop, this paper has sought to provide an overview of what is known about age-skill profiles and to conduct an analysis that demonstrates how trend data based on repeated cross-sectional observations of direct measures of skill at the cohort level can be used to estimate skill gain and skill loss over the lifespan and over time.