An international collaborative research group including Tokyo Institute of Technology, Universite PARIS DIDEROT and CNRS has discovered that CO2 is selectively reduced to CO when a photocatalyst composed of an organic semiconductor material and an iron complex is exposed to visible light. They have made clear that it is possible to convert CO2, the major factor of global warming, into a valuable carbon resource using visible light as the energy source, even with a photocatalyst composed of only commonly occurring elements.