The Porsche 996 is the internal designation for the Porsche 911 model manufactured with first model year 1999 and last 2004. It was replaced by the Type 997 in model year 2005.
The 996 had little in common with its predecessor, with the first new chassis platform since the original 911 and a new water-cooled engine. Technically, it was a major change, a complete breakaway from the original car other than overall layout.
Development was shared with the earlier Boxster including the entire front end and front suspension, much of the interior, and the engine was an enlarged development of the Boxster unit. However the multi-link rear suspension, derived from the earlier 993, was different.
At its debut, the 996 featured the most significant change from the classic 911 series, a water-cooled engine replacing the previously air-cooled engine. Progressively stringent emissions and noise regulations, environmental concerns, a higher expectation for refinement and a high-performance 4 valve per cylinder engine made the switch necessary. Other major changes include a completely new platform having a sleeker body with a more raked windshield, and re-designed interior. (Wikipedia)