The behavior of charged interfaces in contact with aqueous solutions has, in recent years, become of great interest in electrochemistry, colloid science and biophysics. This topic is closely connected with the state of hydrated ions which are accumulated at such interfaces due to electrostatic and specific adsorption forces. The state of water at the interface of its liquid phase with its vapor (air), non-conducting or semi-conducting solids (oxides, AgI etc.), and with charged and uncharged metallic phases (electrodes, is examined. From the thermodynamic point of view, the excess entropy of water at the air/water and electrode/water interfaces provides specially useful information on the state of water at these boundaries. At the air/water interface, Stefan's ratio provides interesting information on the state of bonding and coordination in the interphase in relation to that in the bulk. The surface excess entropy of liquids, including water, is shown to be a function of the cohesive energy density of the fluid. The surface excess entropies and energies are related in a compensating way (compensation principle). The evidence for long-range structuring of water at interfaces is critically examined; it is concluded that little sound thermodynamic or other evidence exists for this supposed phenomenon. In the case of charged metal interfaces, the state of water has been treated at three levels in terms of (a) continuum dielectric theory; (b) H 2O dipole orientation and (c) polarization and orientation of H-bonded clusters of water molecules. The models on which these treatments are based are critically compared in relation to recent conclusions on interactions and structure in the bulk water solvent itself. The inner-layer capacitance contribution, which charge-dependent orientation of water molecules gives rise to, is examined in relation to (a) experimental evidence for H 2O dipole orientation given by studies of displacement of adsorbed water by non-polar organic molecules; (b) work-function and potential of zero charge changes; and (c) effects arising from interaction between hydration co-spheres of adsorbed ions in the double-layer amongst themselves (Gurney co-sphere effect) and between the ion co-spheres and the oriented water layer at the metal. Hitherto, treatments of the inner region of the double-layer have been restricted, on the one hand, to behavior arising from ion adsorption and two-dimensional ionic interaction with little reference to the water layer and, on the other, to behavior associated only with solvent molecule or cluster orientation, neglecting the presence of ions. It is shown that neither of these types of treatment can be realistic, as cosphere interactions between the adsorbed ions and with the oriented water layer at the metal surface will normally be of major importance in the properties of the double-layer and give rise to the well-known ion-specific inner-layer capacitance behavior of electrodes in aqueous electrolytic solutions. The state of ions at metal interfaces is also determined by the so-called electrosorption valency factor, γ, which measures the extent of charge-transfer involved in an adsorption or ion-deposition process. γ then determines the extent of local hydration of chemisorbed ions and their influence on the oriented water layer. Models for the adsorption of ions and water at colloid and polyelectrolyte interfaces are also examined. Unlike the case of metal interfaces where the charge on the metal side is delocalized, the behavior of water and ions at charged colloids is better treated in terms of an array of water-shared ion pairs, mobile or immobile, depending on the origin of the charge on the colloid.