This Green Book covers a wide spectrum of topics, bringing together perspectives from leading experts in various scientific disciplines, ranging from demography, sociology, psychology and epidemiology, to economics, politics and history. In their short contributions, the authors present evidence that sheds light on these fundamental questions. It is clear that the topics discussed here do not provide a complete picture of the diversity of demographic change, which includes an even wider range of questions, for example, related to family and migration policies. The contributions by these experts should encourage readers to think about how we can deal with the phenomenon of increasing life expectancy and promote an exchange of ideas about one of the most important issues for the future of our society. Because in the end, only one thing is certain: Demographic change.