The author introduces what kind of information on surface, thin film, and nano structures are deduced using x-ray diffraction. Some titles of researches that involved him are listed to give readers the information. He briefly summarizes a main idea of x-ray diffraction and gives the outline from its measurement to modeling a structure. A diffraction-intensity distribution and a shape as well as dimension of respective Bragg conditions are recorded, while structure of a crystalline sample is achieved on an atomic scale through the relation of the Fourier transformation between the real space and the reciprocal-lattice space. He discusses a total structure factor of a sample that is composed of a surface-layer part and a bulk crystal part. The structure factor is expressed using the same coordination, i.e. the same origin and the same in-plane unit-cell parameters, in the real space. Typical measurement methods are mentioned with technical notes. Some results of researches he principally conducted are described.