This book shows how to use supercritical water (SCW) to synthesize nano- andmicro- oxides, inorganic salts and metal particles and its recentadvancement. Also polymer/biomass particles can be produced by using themethod of precipitation of solutes from SCW. The particles can be used ascatalysts for biomass conversions, materials in ceramics & electronic devicesand composite materials. Particles are easily produced continuously ina flow reactor in short reaction times or synthesized in a batch reactor in long reaction times. Besides the synthesis process, the book also present studies of the properties of these materials. The size, size distribution, crystal growth & structure, and morphology of particles produced by supercritical water can be controlled by the feed concentrations, pH, pressures, temperatures, heating & cooling rates, organic modifications, reducing or oxidizing atmospheres, flow rates and reaction times.