The Porsche 911 is a two-door, 2+2 high performance rear-engined sports car made since 1963 by Porsche AG of Stuttgart, Germany. It has a rear-mounted flat-six engine and all round independent suspension. It has undergone continuous development, though the basic concept has remained unchanged. The engines were air-cooled until the introduction of the Type 996 in 1998, with Porsche's "993" series, produced in model years 1994–1998, being the last of the air-cooled Porsches.