Plug-in hybrid electric vehicles (PHEVs) are being developed around the world, with much work aiming to optimise engine and battery for efficient operation, both during discharge and when grid electricity is available for recharging. However, the general expectation has been that the grid will not be greatly affected by the use of PHEVs because the recharging will occur during off-peak hours, or the number of vehicles will grow slowly enough so that capacity planning will respond adequately. This expectation does not consider that drivers will control the timing of recharging, and their inclination will be to plug in when convenient, rather than when utilities would prefer. It is important to understand the ramifications of adding load from PHEVs onto the grid. This book analyses the potential impacts of PHEVs on electricity demand, supply, generation structure, prices and associated emission levels.