By accepting that the world is warming and humans are largely responsible, the Paris climate agreement from December 2015 has provided a powerful impetus not only for climate policy but also for climate research. To address the resulting new challenges, the Cluster of Excellence "Climate, Climatic Change, and Society (CliCCS)" will establish a long-term program spanning the range from basic research on climate dynamics and climate-related social dynamics to the transdisciplinary exploration of human–environment interactions. CliCCS will explore climate change with a broader expertise than at any other center in Germany and worldwide. CliCCS will investigate how the climate changes and how society changes with it, thereby feeding back on climate. Understanding these changes, including how societies adapt, will enable us to assess with far greater confidence than before the range of imaginable climate futures. In taking on this challenge, CliCCS is guided by the overarching question:Which climate futures are possible and which are plausible?CliCCS will identify those climate futures that are possible, meaning that they are consistent with our joint understanding of both climate and social dynamics, and those that are plausible, meaning that we expect them to unfold with appreciable probability. CliCCS will boost the understanding of the crucial natural processes that either enhance or reduce anthropogenic climate change, allowing us to rein in more tightly our estimates of possible climate futures. CliCCS will identify which social dynamics support or prevent the deep decarbonization required to meet the climate targets of the Paris agreement; this will enable an assessment of which greenhouse-gas emissions pathways are more probable than others. CliCCS will comprehensively characterize magnitude and mechanisms of chaotic variability in a warming climate, recently found to be much larger than expected, and will explore how the resulting irreducible (aleatoric) uncertainty can be accounted for in climate-socioeconomic interactions and in decision-making processes. CliCCS will establish an understanding of the competition between climate targets and other societal goals in concrete case studies of sustainable adaption to climate change, by combining possibly unstable social dynamics with the impulses arriving from the physical system marked by unpredictable variability and extreme events.CliCCS will use observations and models of the natural, coupled human–environment, and social systems to understand the processes that govern these systems. The new ICON-based Earth system model, arguably the most modern of its kind worldwide, will provide a powerful and flexible numerical laboratory of the natural Earth system and will allow efficient use of high-performance computing systems at the German Climate Computing Centre. A central CliCCS synthesis will be provided through an expert assessment published annually in a Hamburg Climate Futures Outlook.