Organic/inorganic nanocomposites (OINs) can be potentially used as high-performance capacitors due to their rapid charge–discharge capability along with respectable power density. The coupling effect of the filler/matrix interface plays a prominent role in the dielectric and electric properties of OINs. Along with a review of contemporary theoretical models, recent advances in interfacial optimization to improve energy density through careful interface control and design are also presented. Possible mechanisms that may improve energy density and potential applications for high-energy-density capacitors are also highlighted.