The study of life in extreme environments is at a crossroads for scientific communities - it needs to be multidisciplinary in its content, and interdisciplinary in its execution. While it is of clear interest for astrobiology, it also links to many other scientific domains: biodiversity, ecological theory, evolutionary biology and biogeochemical cycles. Supported by the European Commission Seventh Framework Programme (FP7) and steered by a multidisciplinary committee involving marine and polar scientists as well as astrobiologists and plant biologists, the CAREX project had for main objectives to develop a community identity, catalyse networking and exchange of knowledge within this community and define a transdisciplinary research roadmap for life in extreme environments. The latter was published in April 2011 and prioritises four high-level research themes relevant to all types of organisms evolving in every type of extreme environment. These themes are detailed in subsets of key questions and concrete research activities are suggested for each of them. The CAREX Roadmap also includes an analysis of the research infrastructure and the enabling technologies required, as well as recommendations for outreach and education. As a strategic document, the CAREX Roadmap is a basis for future international collaborative initiatives.