Aqueous precursor solution is often employed to produce metal oxide nanostructures and thin films through the hydrolysis of metal ions. Due to the constraints imposed by being far away from an equilibrium condition of synthetically grown oxides in solution, the degree of crystallinity is low, and the controllability of specific phases and structures can be challenging. It also requires very low supersaturation and a seed crystal, which often makes the process impractical and limited despite its potential as an alternative to vapor/plasma-based processes. A hydrothermal solution processing technique can, however, offer a more precise control of process parameters as a means of tailoring nanostructure developments of TiO2 and its hybrid architecture. Especially, when it establishes the aggregation-driven growth model from oxide nanoparticles precipitated in supersaturated solution, it has potential to produce highly crystalline structures along with a high growth rate even at low temperature and cost. Hydrothermal process is carried out at various temperatures (between 80 and 220 °C) using mixed solvents and various fill levels to gauge the effect of autogenous pressure and liquid density during processing. In particular, there exists a supersaturation level of precursor solutions, below which the growth of high-quality, anisotropic crystals of TiO2 is feasible. For a low degree of supersaturation, nanoparticles or nanowires with high crystallinity can aggregate to form the secondary nanostructures depending on their oriented attachment. Such particle-based crystallization pathways have the potential to produce a single crystalline nanorod array of TiO2 from solution. The surface of these nanorods can be further treated via another hydrothermal method or ion exchange with other oxide phases to form the hybrid structure consisting of a core and a shell. It improved its functional properties compared to those of the original core phase, thereby making the hybrid TiO2 nanostructures well suited for light or pathogen stimuli applications that require excellent photocatalytic, photoelectric, and antimicrobial properties. Importantly, the hydrothermal process provides more sustainable synthetic paths by offering low temperature, low energy consumption, and less toxic precursors.