The EU-funded ATHLOS Project aims to achieve a better understanding of ageing by identifying patterns of healthy ageing trajectories, the determinants of those patterns, the critical points in time when changes in trajectories are produced, and to propose timely clinical and public health interventions to optimise healthy ageing. Moreover, a new definition of ‘old age’ based on many characteristics rather than just the classical chronological definition of age will be used for calculating projections in each specific population and guide policy recommendations. The new definition will be used for calculating projections in each specific population and to guide policy recommendations.