City regions and metropolitan areas form the scale on which the battle for will be won or lost, and the level at which cities can become resilient and even self-sufficient. A master plan for a sustainable energy system for city regions is not a luxury anymore. An energy master plan will be based on incremental steps of transition. The approach needs to start with the charting of energy sources, sinks and unused potentials of a studied area. Herein the method of Energy Potential Mapping can play an essential role. The next step deals with the identification of demand reduction possibilities in the existing built environment – new construction can already be zero energy. Differences in simultaneous discrepancies between supply and demand can be bridged by synergetic systems, heat exchange, cascading and intermediate storage of energy. Finally the remaining demand needs to be solved with renewable energy, inside the city as well as in its environs, which become ever more indispensable to the modern metropolis. In the energy master plan EPM deals with the identification of supply and demand, supports the finding - in place and time - of energy potentials from sun to magma, helps the discovery of simultaneous mismatches, surpluses and shortages, and helps determine the effect on the urban climate. Mapping is done in 3D, soon to be 4D, including the time factor (diurnal differences, seasonal differences, long-term developments). Since 2005 Energy Potential Mapping has been developed at TU Delft. It has gained international scientific standing. The advanced 3D method has been used for sustainable energy plans and currently forms the basis for making Dutch regions energy-neutral, in cooperation with local stakeholders. The full paper will describe the Energy Master Plan approach and Energy Potential Mapping method, illustrated by cases executed so far.