Populations globally are changing in fundamental ways. A result of the demographic transition, or the shift from high to low mortality and fertility rates, the slower population growth is accompanied by a shift in population age structures. Never before in history have so many people of different age cohorts been living together. This paper, prepared jointly by the five regional commissions of the United Nations, explores the social and economic challenges and opportunities of demographic shifts towards multigenerational societies across the countries covered by the five regional commissions. It discusses the latest evidence on demographic trends and intergenerational relations, labour markets, social protection, care, living arrangements and digitalization across regions, and it provides recommendations to build societies for all ages. With a strong interdisciplinary and interregional focus, the paper addresses intergenerational relations from a variety of perspectives and highlights common actions required, while also acknowledging regional differences. This paper was launched by the regional commissions on the sidelines of the Summit of the Future on 21 September 2024.