Engine

• Every hybrid has a traditional gasoline engine. Fuel-sipping models use a small engine to get the best mileage. Larger hybrids have a bigger engine so performance isn't sacrificed.
  
  

Motor

• The gasoline engine shares duty with an electric motor. Its power is usually a fraction of the engine's and has much better energy efficiency. The electric motor runs primarily during city driving, making best use of its efficiency.
  
  

Batteries

• The electric motor is powered by a large bank of rechargeable batteries. Carmakers use a variety of battery technologies such as lithium or nickel-metal hydride. In addition, the car might use a standard 12-volt automotive battery.
  
  

Controller

• The controller, or engine management, is a key part of the hybrid design. A computer monitors driving conditions, battery status and other factors to determine if the car runs on the engine or the electric motor. Successful designs switch back and forth smoothly and efficiently.
  
  

Braking

• In a conventional car design, the energy of the car's movement becomes wasted as heat when the driver applies the brakes. With a hybrid, this energy is recaptured to charge the battery. This greatly improves gas mileage for stop-and-go urban driving.