The Porsche 911 is a 2-door high-performance rear-engine sports car that has been on the market since 1963. Over the years it has undergone extensive development, however, the basic concept for the vehicle has remained largely intact. The Porsche 911 has been available in multiple body styles, including the 2-door coupé, 2-door convertible, 2-door Targa top, and 2-door speedster. One of the biggest changes made on the Porsche 911 is that it went from having air-cooled engines up until 1998 when they switched to water-cooled engines, which they still maintain to this day.