One of the more exciting advanced vehicle designs of recent years is the plug-in hybrid-electric vehicle (PHEV). Its ability to run on electricity from the power grid can reduce both the vehicle’s fuel consumption and emissions of various pollutants relative to current vehicles. The extent of these benefits, however, will depend heavily on a handful of important factors, including the fuel mix used to generate grid-based electricity, vehicle battery size, the vehicle’s operational logic, and the vehicle’s drive cycle characteristics. Meanwhile, central to the economic viability of these vehicles is the status of advanced battery cost and performance. This popular report looks beyond the hype to assess the environmental and economic potential of this exciting new vehicle design.