The review discusses the properties of RTILs at different EIs, specifically the RTILs' response to charging of the interface and how it manifests itself in a range of selected applications. Response of an electrolyte to a charged electrode surface is described within the theory of electrical double layer (EDL). It overviews the current status of the theory of EDL in RTILs, showing that the structure of EDL there is different from that of a diluted electrolyte despite having certain common features with that of high-temperature molten salts (HTMS). It is well-known that the EDL plays a crucial role in electrodes and the potential drop across the EDL and its response to charging determines the electrical capacitance of the electrode/electrolyte interface and the energy stored in the EDL capacitors. The potential distribution in the EDL controls electrochemical kinetics, as the voltage difference between the electrode and the point where the reactant sits is the driving force of electrochemical reactions.