Hybrid electric vehicles (HEVs) combine both a standard internal combustion engine with a smaller electric motor. HEVs do not need to be plugged in. Rather, batteries store electrical energy and are charged by an onboard generator or by regenerative braking. This process is similar to recharging the alternator in a conventional vehicle. In city driving conditions around 30% of a typical car engine's outputs is lost to braking; some of this energy can be recovered in the battery.

Hybrid vehicles can be designed in a series configuration, a parallel configuration, or a combination of both. In a series design, energy from the internal combustion engine along with energy regained from generators and/or breaking is converted into electrical energy, which is stored in battery packs. An electric motor is used to drive the wheels. The electrical engine is used during idling or traveling at low speeds.

Most hybrid vehicles on the market today are small to medium sized cars. However, more recently pickup trucks, sport utility vehicles, and even transit buses and utility vehicles are being produced with hybrid engines. Hybrid engines are ideal for stop-and-go-driving conditions such as city driving, transit buses, and service/delivery trucks.