What Is a Hybrid Car? How Do Hybrids Work?

What could a Toyota Prius possibly have in common with a Cadillac Escalade, Chevy Silverado or Ford Fusion? Each is available with a hybrid powertrain, a propulsion system made famous by the Prius. While consumers benefit from the improved fuel economy, hybrids give automakers a way to meet ever-tightening Corporate Average Fuel Economy (CAFE) requirements and proposed limits on carbon dioxide (CO2) emissions.

But what exactly is a hybrid, and how do they improve fuel economy? Are all hybrids laid out essentially the same under the hood, and do they all provide similar fuel savings?