Learning from the concepts used by green plants photosynthesis, we have developed nanostructured systems affording efficient solar light harvesting and conversion to electricity and fuels. Solar cells using dyes or semiconducting nano-particles as light harvesters supported by mesoscopic oxide films have emerged as credible contenders to conventional p-n junction photovoltaic devices. Separating light absorption from charge carrier transport dye sensitized mesoscopic solar cells (DSCs) were the first to use a three-dimensional nanocrystalline junction for solar electricity production. The standard AM 1.5 solar to electric power conversion efficiency (PCE) has reached 12.9% for laboratory cells and 9.9 % for PV modules. PCEs over 25 % are attained under ambient and indoor light conditions. These features along with excellent long-term stability have fostered first commercial applications, the industrial production of DSC’s attaining presently the multi MW/year scale. Striking advances in the direct generation of fuels such as hydrogen from water and sunlight have been achieved by the judicious design of photosystems composed of nanostructured Fe2O3 or Cu2O.