This chapter is divided into three sections: Introduction, SAXS technique and SAXS applications. The introduction gives a brief description of the X-ray scattering basics, which includes the classification of scattering systems, the SAXS intensity, and the gyration radii of some scatters with specific shape. In the second section, the SAXS techniques including the normal SAXS, WAXS, and USAXS with transmission mode, the GISAXS with reflection mode, and the ASAXS with energy-scanning mode are simply mentioned. Some typical application examples of the SAXS techniques are described in the third section. Five main areas of SAXS applications including biological macromolecule, phospholipids and micelles, polymer and related materials, nanomaterial and superlattice, as well as natural biomaterials are discussed. Shape analysis of scatterers, complex and assembly, in-situ processes, size distribution of scatterers, and hierarchical structure are emphasized in the above five application areas, respectively. Finally, the methods and applications of ASAXS and GISAXS techniques are also presented briefly in the third section.
