The interplay between the structure and composition of the electric double layer and the surface charge controls the electrocatalytic activity of reactions central to decarbonization of chemical fuels and materials. The employed electrolyte can affect the charge distribution and the electric field on the interface, which also alters the local pH and ordering of the water-solvent network. Additionally, the electrolyte plays a key role in stabilizing or destabilizing the adsorbed intermediates via non-covalent bonds, or poisons the surface and induces surface reconstruction, affecting the reactivity of the active sites positions. Herein, we discuss, from an experimental perspective, electrolyte effects on different interfacial properties relevant to electrocatalysis.