Tandem-L is a proposal for a highly innovative satellite mission for the global observation of dynamic processes on the Earth’s surface with hitherto unknown quality and resolution. Thanks to the novel imaging techniques and the vast recording capacity, Tandem-L will provide urgently needed information for solving pressing scientific questions in the areas of the biosphere, geosphere, cryosphere and hydrosphere. Tandem-L will make a vital contribution towards a better understanding of the Earth system and its dynamics.