Novel hydrothermal solution processing routes covering conventional hydrothermal, solvothermal and supercritical hydrothermal techniques are becoming the most efficient routes for advanced nanomaterials processing including the high melting compounds. The importance of these novel hydrothermal solution routes has been discussed with appropriate examples. The current trends in the hydrothermal solution processing of materials, the importance of solubility study, thermodynamic calculations and the role of surfactants and chelates have been discussed in detail. The multi-energy processing of materials, instant hydrothermal system and the new concept in materials processing, viz. Chemistry at the speed of light have been highlighted here. The hydrothermal synthesis of nanomaterials of carbon polymorphs, rare earth vanadates, metal oxides and their nanocomposites have been discussed with an emphasis on the control of size and morphology.