Beyond activated carbon and other forms of high-surface area carbon operating solely as double layer storage materials in capacitors of high capacitance commonly somewhat imprecisely called supercapacitors other electrode materials storing electric charge by reversible and fast superficial redox processes are studied as active masses. The resulting devices combining double layer and Faradaic process-based charge storage -commonly called hybrid ones -show significantly higher capacitances at only marginally diminished power capability. Among the suggested materials metal oxides feature most prominently. Their formation, characterization and properties together with the performance of prepared devices are reviewed here.Electric energy cannot be stored directly in amounts large enough to gain commercial viability. Systems employing e.g., superconductors or dielectric capacitors are either too large or too expensive in order to be of any wide importance (for examples and a brief review see [1]). Thus, basically two modes of rather direct storage employing chemical, more specifically physico-chemical, and electrochemical principles remain: Storage based on charge separation in the electrochemical double layer (i.e., capacitors) or storage based on the reversible conversion of electrical into chemical energy and vice versa A+ B C+ D: the accumulator (see Fig. 1).For various reasons the former mode has for a long time been associated with high power mostly because of the inherently fast processes leaving out any interfacial electrochemical reaction limited by the inherent constraints of interfacial processes and the latter with high energy because of the much larger amounts of energy which could be stored based on associated chemical conversion reactions. This is also the inherent reason of the lower power of the latter devices, interfacial reactions mostly associated with phase transformations and extended transport of matter tend to be slow. The energy density of the former devices tends to be low because of the limited amount of interfacial surface area available in any given device. This is illustrated in a Ragone plot showing some examples of storage devices (see Fig. 2).As indicated devices based on traditional electrolytic capacitor technologies (as in aluminum foil-or tantalum-pentoxide-based ones) show highest power density. Although these devices are based only on the movement and separation of electric charges without any chemical reaction being involved a short characterization of salient features may be helpful to settle the current confusion about these various devices.