World population continues to increase: it passed the 8-billion mark last November and is projected to top 10 billion this century. However, fertility rates are dropping across the board and global population is ageing fast. In the face of declines in working-age population, countries are called to find ways to reform their pensions and welfare systems. Meanwhile, some world regions such as Sub-Saharan Africa are still experiencing very high population growth rates, which could hamper development. As the world gets even more crowded this century, what recipes to increase sustainability? How to support economic growth in a world that is rapidly ageing?