Past4Future will combine multidisciplinary paleoclimate records from ice cores, marine cores, speleothems, pollen and other records, concentrating on a global distribution of the records, to reconstruct climate change and variability during the present interglacial (the Holocene) and the last interglacial (known as the Eemian in northwestern Europe and as marine isotope stage 5e in the marine sediment records). The records will be combined in integrated analyses aided by proxy modeling and assimilation, to gain understanding of the climate processes involved in the dynamics of interglacial climates. Earth system models (ESM) including physical and biogeochemical processes will be applied to simulate the past and present interglacial climate, and to confront and intercompare the simulations with climate changes as observed from the palaeodata; this will both advance the models and our understanding of the dynamics and predictability of the climate system. Focus will be on the most recent two interglacial periods, as these provide the highest-resolved most comprehensive data records. Moreover the last interglacial represents a situation where the mean state was warmer than at present in large regions due to orbital forcing, thereby allowing tests of climate system sensitivity to constrain projections of potential future ice sheet, sea-level, circulation and biogeochemical changes. The data and Earth system model results will be used improve our capabilities to project future global and regional warming from a better understanding of relevant paleoclimates, especially in relation to sea level changes, sea ice changes and thermohaline circulation changes.The Past4Future program will draw together a world leading team of European and international partners in a concerted effort to advance our knowledge on the causes, processes and risks of abrupt changes in warm periods, such as those projected for the current and the next century. The program will inform the international debate on climate system stability and the dissemination of results will be targeted to both citizens and governmental and non-governmental stakeholders. It will leave a legacy of improved understanding of past drivers of sea level changes, changes of sea ice, and of greenhouse gas concentrations, and it will train a new generation of young climate researchers to further advance research and improved future predictions for the benefit of society and our capacity to mitigate and adapt to climate changes.