Summary form only given. The Microwave plasma assisted CVD synthesis of diamond was first demonstrated during the early 1980s by Kamo et al [1]. Diamond synthesis was achieved in a small ( 2-4 cm ), tubular reactor where microwave energy was coupled into a quartz tube that was inserted through a waveguide. This reactor produced high radical densities and high quality diamond films and was inexpensive, simple to design, construct and operate. Hence it was utilized by many early diamond researchers to experimentally investigate and understand CVD diamond synthesis. However this reactor type had a number of inherent limitations such as small deposition area and low operating pressure regime. Since these early investigations the significant potential of industrial applications of CVD diamond synthesis has spurred numerous, innovative, microwave plasma reactor designs. In view of the important, recent, opportunity to commercially synthesize a variety of high quality diamond materials, i.e. nano crystalline diamond, polycrystalline diamond and single crystal diamond, there is a need to further improve existing designs and to develop entirely new microwave plasma-assisted reactor designs that are able to achieve diamond synthesis at high rates and over large areas. For example, certain applications require large (12-20 cm diameter) deposition areas, while other applications require high rates (30-50 micron/hr) and often some reactor users desire large areas, high rates and very high quality. Since it is important to increase deposition rates it is desirable to develop and optimize new reactors and processes in the 100-300 Torr pressure regime. This presentation will look at microwave plasma reactor design in view of the need for operation in the 100-300 pressure regime. In particular the following will be discussed: (1) the "basic physics" behavior of the microwave discharges at high pressure, (2) microwave discharge stability, (3) the thermal management of the substrate environment, (4) reactor design using computational modeling, and (5) the trade off between large area deposition uniformity and high growth rates. Technologies that yield large area, uniform, high rate, high quality and controllable deposition will be described.