Hybrid, applied to vehicles, implies multiple motive power sources. A hybrid electric vehicle (HEVs) uses both an IC engine and an electric motor to power the vehicle. When modern hybrids were introduced in the late 1990s, they were initially characterized as a technology bridge from fossil fuel combustion to all-electric propulsion. But with the introduction of plug hybrid electric vehicles (PHEVs) circa 2007, they have taken on a new role as an all-around solution that can meet the needs of the majority of vehicle owners, providing the high efficiency and zero emissions of an electric motor, the energy-recovering capability of regenerative braking, and the refueling options of both gasoline and electric charging, without the high cost and weight, reduced range, long recharge time, and additional safety concerns of battery electric vehicles (BEVs). In this chapter, the history of hybrid electric vehicles starting in the nineteenth century is briefly reviewed. The associated innovations in power electronics, controls, and power-split drivetrains make up the majority of the chapter, culminating with a review of current vehicles and technologies.