Abstract: The preparation of functional materials in supercritical solvothermal conditions will be discussed from a chemistry prospective. I will focus on the description of in situ characterization techniques developed to monitor in real time phenomena such as fluid dynamics, thermodynamics, chemistry, and particle nucleation and growth. This presentation will emphasize how the coupling between these chemistries and chemical engineering gives access to the formation of unique and high-quality nanostructured materials. The mastering of the chemistry coupled with one-pot multistep processes opens the road toward the continuous design of multifunctional materials as illustrated with functional layered double hydroxides. The benefits of the sub- and supercritical continuous solvothermal route include not only better performances for advanced applications but also more environmentally friendly syntheses.