Here, we consider the equilibrium properties of the electric field profile at the interface between a solid surface and a dilute electrolyte solution (e.g., ionic concentration of ∼ 10 0 -10 -2 M). Due to the physical consequences of ionic screening, these fields are only appreciable within a narrow region of space extending less than 1nm into the liquid. This molecular scale region is extremely difficult to isolate via experiment, which is why our current physical understanding lags significantly behind that for bulk systems. Electrochemical measurements report accurately on the electrostatic potential differences on either side of a solid-liquid interface, Interfacial electric field profiles are then derived from theoretical models that prescribe the shape of the electrostatic potential profile that spanning the interface, as illustrated in Fig. . Electrochemical measurements report on the potential difference, ∆Ψ, across a solid-liquid interface. Theoretical models are required to describe the shape of the interfacial potential profile (red lines). The electric field profile is then given by the negative gradient of the electrostatic potential. Different models thus predict different interfacial electric field profiles.