The role of science as a provider of well-tested and trustworthy knowledgre in a sustainable society is discussed with respect to other social institutions: government and state bureaucracy, the market, the media and the public. In particular, societal pressures that threaten scientific endeavour are problematised with a slight bias towards examples from sustainability science. Global challenges of today transcend social institutions and therefore require novel modes of trans-institutional cooperation. Such modes of cooperation may produce unwanted clashes of institutional norms that imperil objective and mutually accepted norms need to be developed. The science policy for a democratic, sustainable society should strive for clear divisions among social institutions while encouraging suitable modes of cooperation to address global challenges to the sustainability of human life.