This IET briefing document explains what a smart grid is and why it is different from the existing electricity grid. It explains why the move to low carbon electricity with significant amounts of variable wind generation will require new ways of balancing the electricity grid. The already-sophisticated transmission network will become smarter still and include greater inter-connection with other countries. At the local distribution network level the changes will be even more profound as low voltage networks, originally designed for one-way flow, will require the measurement and control capability to accept input from solar panels and other small scale renewable generation while also supplying larger demands for electric vehicle charging or heat pumps. A smart grid will enable these changes to be made efficiently with disruption from costly network re-enforcement kept to a minimum. Consumers will increasingly play a part in reducing peaks in electricity demand by varying their demand in line with the availability and being rewarded for doing so. The briefing includes the role of smart meters in a smart grid and brief case studies of smart grid developments in the UK and the rest of the world.