The molecular study of liquids is a field that recently has had a strong development, both, because of the appearance of new experimental techniques, and the increasing power of computers. Here we present a study of hydration looking into the molecular basis of the phenomenon. We compare the molecular patterns involved in aqueous solutions ofMg2+, Urea, and Methanol. All studies were performed by Monte Carlo simulations, using highly refined potentials. Care was taken on including polarization and nonadditive effects. We present an analysis of the different contributions to the hydration energy, coming from solute‐water interactions, or modification of the water–water interaction as a result of the presence of the solute. We also present the structural consequences of hydration, from the very dramatic ones for the ion to the very small ones for urea. Of course the main interest is in gaining understanding of hydration. We advance proposals such as: a) that electrostriction is a very local effect, due to the hydration shells of the ion rather than changes in the density of the solute, b) the coexistence of a urea network with the water network and c) the very small disruption by methanol of the water network.