In early 1996, over six years into the life of the R129, development work on a successor began. On 27 January 1996, design work commenced and draft designs were submitted from ten designers in Germany, California, and Japan. Hundreds of sketches were submitted and would form the basis for twelve quarter scale models which were digitized for computer manipulation. Design of the R230 would progress through two different formats. The real world process centered on the traditional 1:4 scale models, with most of them initially being done clay. Virtual world design development took place in a room packed with state-of-the-art computer processing technology referred to as the “CAVE” (Computer Aided Virtual Environment). This technology was also used earlier on to design the W203 in 1995.
The supercomputer in the “CAVE” was able to create full-size images of selected designs, using its five projectors and allowing designers to inspect every inch of every surface rendered. Parallel to the virtual process, the twelve scale models were scrutinized as well, with four standouts chosen to be created in full-size mockups. This evolution of the scale models occurred alongside the development of the interior design. On 16 June 1997, the final design for the R230 was approved by the board and refined into production specifications into 1998. The design patents for the R230 were later filed in Germany on 9 September 1999 and on 1 March 2000 in the United States.
In July 2001, after over five years of development, the new SL was unveiled and introduced at the 2001 Frankfurt Motor Show that September. Production began on 13 October 2001 at the Bremen plant and European sales commenced that November.