Existential challenges of the twenty-fi rst centuryThroughout history mankind has caused unintended changes in the natural environment, including phenomena such as extinction of vulnerable species and soil erosion from deforestation ( Crosby, 2015 ). These changes, however, were confi ned to local or regional scales. Unprecedented in the twenty-fi rst century is that science and technology associated with industrialization, whilst they have further transformed the conditions of life for humanity, now create environmental impacts at the global scale. Our socio-industrial-agricultural metabolism and land-cover changes are signifi cantly altering the earth system's natural bio-geo-chemical cycles and threaten the integrity of the biosphere, which both when unperturbed contributed to maintain the relatively stable conditions under which humanity has thrived over the last 10,000 years.The existential problems of the human civilization in the twenty-fi rst century are complex as they relate to interactions between humans and their environment in a world that is experiencing accelerating changes in the technological, cultural, political, economic, and environmental spheres. Moreover, changes in all these spheres are globally interconnected and interdependent. Traditional disciplinary fi elds of 'normal' science and static approaches to management and governance relying on prediction, regulation, and control can play only a limited role in resolving such complex problems. Experts in different fi elds of knowledge in the natural and social sciences often fail to understand each other, and we are drowning in specialised expert reports that often do not suffi ciently account for interdependencies and feedbacks between changes in these different spheres. New approaches to combining knowledge co-creation and distributed governance should be designed to enable the effects of human-environment interactions to be continuously and iteratively monitored, evaluated, judged, and acted upon, based on social norms that respond to locally determined sustainability issues. This book's main premise is that one of the most fundamental challenges we face as we are affecting the functioning of the entire planetary system, is to develop new approaches to knowledge co-creation and governance that will enable us to relate to our environment and to each other in view of more complex interdependencies between local and global circumstances, in how we conceive of the natural and social worlds, now and in the future. The silo-based approach to science and expertise, government and practice, with strict separation of research in the natural sciences and social sciences and the humanities that has co-evolved with industrialization, is no longer adequate for our civilization to cope with twenty-fi rst-century challenges. New approaches to combining research, governance, and learning in 1 Sustainability science as a transformative social learning process