Aqueous electrolyte solutions confined to the nanoscale are important for numerous technologies, whether it be the highly porous electrodes found in batteries and supercapacitors or the nanostructured membranes used for water desalination, dialysis, and other separation processes. The behavior of each of these technologies is highly sensitive to the nature of ion-ion interactions in the electrolyte. In supercapacitors, for example, the accessible charging and discharging rates of the device are determined in part by the conductivity of an electrolyte confined within a porous carbon electrode; this conductivity is significantly impacted by the extent to which ions exist as free charge carriers versus neutral ion pairs. Ion-ion interactions also impact the electrolyte's transference number, i.e., the relative flux of each ionic species, and thus have important implications in designing membranes for ion-selective separations. Understanding and ultimately controlling ion pairing behavior in nanoconfined solutions is thus a crucial element of developing improved energy storage and separations technologies.