Resonant x-ray scattering (RXS) is a very powerful technique to detect the charge distribution and magnetization density with a synchrotron radiation source. Recently this technique has been applied to study charge-, spin-, and orbital-orderings in strongly correlated electron systems. In this paper the cross section and the scattering amplitude of RXS are given on the basis of the interaction between electrons in matter and electromagnetic wave.The atomic scattering factor becomes a tensor instead of a scalar through the resonant process. Charge and orbital orderings of perovskite manganites have been studied using the RXS technique. It is shown that the RXS intensities have characteristics in energy, polarization, and azimuthal angle dependences. Finally an outlook for the RXS technique is briefly mentioned.
