After a commentary on the fundamental aspect of the voltammetry for charge (ion or electron) transfer at an interface between two immiscible electrolyte solutions, applications of the voltammetry to the elucidation of interfacial phenomena accompanied by charge transfer reactions are reviewed focusing the attention to the relation between characteristics of transferring ions and half-wave potentials, ion transfer facilitated by ionophors or surfactants, the fundamental feature of interfacial electron transfer, ion transfer coupled with electron transfer at an interface, the relation between half-wave potentials and extraction constants in ion-pair extraction and the oscillation of the interfacial potential during ion transfer. The voltammogram for ion transfer through a liquid membrane is also introduced and, comparing the voltammogram with voltammograms for ion transfers at two aqueous/membrane interfaces in the membrane system, the membrane potential is connected to the potential differences at two aqueous/membrane interfaces. The ion transfer through a bilayer lipid membrane (BLM) is discussed referring to that through the liquid membrane. The mechanisms of oscillations of membrane potential and current which have been discovered recently by the author et al. are discussed based on the voltammogram through a membrane.