This review highlights the frontier scientific research in the development of polymer nanocomposites for electrical energy storage applications. Considerable progress has been made over the past several years in the enhancement of the energy densities of the polymer nanocomposites via tuning the chemical structures of ceramic fillers and polymer matrix and engineering the polymer-ceramic interfaces. This article summarizes a range of current approaches to dielectric polymer nanocomposites, including the ferroelectric polymer matrix, increase of the dielectric permittivity using high-permittivity ceramic fillers and conductive dopants, preparation of uniform composite films based on surface-functionalized fillers, and utilization of the interfacial coupling effect. Primary attentions have been paid to the dielectric properties at different electric fields and their correlation with film morphology, chemical structure, and filler concentration. This article concludes with a discussion of scientific issues that remain to be addressed as well as recommendations for future research. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1421-1429, 2011