Since the introduction of powerful computers, numerical simulations were used to provide a molecular basis to the interpretation of complex physico-chemical phenomena observed at the solid/liquid interface. Generally based on a double quantum and statistical approach, Monte Carlo and Molecular Dynamics simulations were successfully exploited to understand, interpret and sometimes predict a large class of mechanical, structural and dynamical properties of such complex interfacial systems. This paper focuses on the clay/water interface because of its use in many industrial applications, but the same molecular approach may be exploited to analyze a great variety of solid/liquid interfaces including not only mineral and metallic oxides but also solvated proteins and biomolecules.