Mitsui Engineering and Shipbuilding Co., Ltd. (MES) has completed and delivered the first commercial plant in the year 2000 at the Yame Seibu Clean Center and the second one in the year 2002 at Toyohashi Waste Treatment of Recovery & Resource Center, based on its Recycling 21 (R-21) pyrolysis and melting technology for municipal solid wastes. The basic technology is licensed from Siemens, but MES have made major improvements to the design and operation of the system and, up to now, have been awarded six (6) R-21 projects including Yame and Toyohashi plants in Japan. The following text will provide a brief overview of the design & operating features of R-21 technology which have been proved by the successful operation experience of Yame and Toyohashi plant.