Ageing populations, changing labour markets, and climate change are affecting economies and societies across OECD countries. What challenges do these "megatrends" pose for social protection systems? What are the implications of these trends for the coverage, the effectiveness, and - critically - the funding of social protection today and tomorrow? With an eye towards informing future reforms, this report presents a broad stocktaking of population ageing, changing patterns of labour supply, new and emerging employment forms, changes in household composition and unpaid work, the effects of new technologies on employment and wages, and the effects of climate change and the net zero transition on social protection systems in OECD countries.