Energy for a modern society must be affordable, reliable, and sustainable. ‘Future energy systems’ considers future electricity generation and electricity networks, including the Smart Grid. Electricity systems are expensive and the choice of technologies to be used is heavily influenced by their costs. Low carbon generation, such as nuclear and renewables, is particularly capital intensive. Local energy systems and microgrids are also considered alongside future gas systems. It is now being recognized that for the development of low carbon energy systems a more integrated and regional approach to energy supply is likely to be preferable. There are no short-term easy solutions to energy supply and all choices involve compromise.