Technological advances have led to the constant development of new techniques to optimise conventional chemical processing technologies. These efforts are relevant because they have produced a wide range of inorganic materials with new functional properties. One research subject that has garnered increased interest from several groups worldwide during the last three decades is the morphological aspect of powder and particulate materials. As a result, significant efforts have been made to investigate new techniques suitable for processing particles on a nanometric scale. Hydrothermal processing has emerged as a prevalent method for rapidly processing nanostructured particles of multiple inorganic compounds for various technical applications.This Special Issue highlights the cutting-edge strategies conducted by several research groups specialising in hydrothermal processing. These strategies are based on fundamental studies on producing nanoparticles using specific chemical reaction conditions, analysing reactant precursors, process intensification, new particle morphological characterisation techniques, nanofluid functionality, and other topics. This reprint provided relevant information to motivate young researchers to continue developing environmentally friendly hydrothermal processing methods for sustainable materials.