The Porsche 911 (pronounced as Nine Eleven, German: Neunelfer) is a sports car made by Porsche AG of Stuttgart, Germany. The famous, distinctive, and durable design is notable for being rear engined like the Porsche-designed Volkswagen Beetle it had been based on. It was also air-cooled until the introduction of the all-new Type 996 in 1998. Since its introduction in autumn 1963, it has undergone continuous development.

Since its inception the 911 has been modified, both by private teams and the factory itself, for racing, rallying and other types of automotive competition. It is often cited as the most successful competition car ever, as the normally aspirated 911 Carrera RSR in the mid 1970s has won major world championship sports car races such as Targa Florio, Daytona, Sebring or Nürburgring outright even against prototypes. The 935 turbo also added the coveted 24 Hours of Le Mans in 1979.

In the international poll for the award of Car of the Century, the 911 came fifth after the Ford Model T, the Mini, the Citroën DS and the Volkswagen Beetle. It is the most successful surviving application of the air (now water) cooled opposed rear engine layout pioneered by its original ancestor, the Volkswagen Beetle, having increased its original 25 PS more than tenfold, or 30fold in turbocharged race cars. It is the third-oldest sports car nameplate still in production, behind the Chevrolet Corvette, and the Nissan Skyline.