This paper systematically discusses the design and control methodologies of a plug-in hybrid electric vehicle (PHEV). Design methodology is focused on battery energy and power capacity design. Two kinds of typical batteries, namely, NiMH and Li-ion, are discussed. Control strategies focus on all electric range and charge depletion range operations. In addition, a constrained engine on and off control strategy is discussed for charge-sustained operation. Simulation has been performed for an example passenger car. The simulation results indicate that a significant amount of fuel can be displaced by electric energy in typical urban driving.