Most developed economies face a triple challenge of sustainability. Financial: ageing of the population puts great pressure on the financial sustainability of the welfare state and public budgets. Social: in most countries income and wealth inequality has increased substantially in recent decades. And ecological: a climate crisis is looming. This project brings together a body of research on optimal policies to address this triple challenge. Macroeconomic efficiency and the potentially conflicting interests of current versus future generations, and of low-skilled versus high-skilled people, should be optimally reconciled. Methodologically, the research is conducted primarily using quantitative macro models with heterogeneous agents (e.g., OLG models with an extended policy block). In addition, econometric panel data research is employed.