Hybrid Technology

History

Hybrids have been in development since 1899 when Ferdinand Porsche created the first working prototype. Engineers took another look in the 1970s due to the oil crisis and rising gas prices. However, no real production models were ever produced until the 1990s. The first models were the Toyota Prius and Honda Insight.

Today

Current gasoline-electric hybrid technology is based on supplementing a standard gasoline engine with at least one electric motor. The electric motor is used at low speeds and lets the vehicle shut down the gasoline engine when stopped.

Energy for the electric motor is gained mostly through the use of "regenerative braking." When a car slows down with traditional brakes a tremendous amount of energy is lost as heat due to friction. Regenerative brakes are essentially a motor acting as a generator. The energy used to produce the electricity is naturally removed from the motion of the vehicle (conservation of energy.)

The cars with the largest mileage improvements (Prius and Insight) also use other technologies to improve performance. These include aerodynamics, smaller size and more efficient tires. Non-hybrids could leverage these as well.

Here are two sources containing more details:
How Hybrids Work - HowStuffWorks.com
Information and history of Hybrids - Wikipedia.org

Future

Over time as hybrid technology improves more vehicles will move down the spectrum from Non/Mild Hybrids to Full Hybrids. Gasoline engines in these vehicles will keep decreasing if gas prices continue rising. Ultimately hybrids are stepping-stone technology to ease the transition from fossil-fuels to either pure electric or other alternative fuel motors.