In this study, we reviewed the selective adsorption and irreversible fixation of cesium (Cs+) on day minerals. The selective adsorption of Cs+ results from reactions with frayed edge sites (FES) of clay minerals. The content of FES is about 0.1-2.0% of the total cation exchange capacity (CEC). The fractionation of Cs+ in actual accident sites mainly exists as a residue, which is important because it is closely related to the strong binding between Cs+ and soils. Cs+ adsorbed onto FES can move into the deeper interlayer via weathering processes, thereby Cs+ can be irreversibly fixed in the interlayer of non-expanding 2:1 layered day mineral. Additionally, Cs+ can be adsorbed in the interlayer of the expanding clay mineral and can be fixed by interlayer collapse. For this reason, Cs+ adsorption onto FES is defined as 'selective adsorption' subsequent sorption in the interlayer as 'irreversible fixation'. Furthermore, the extended X-ray absorption fine structure (EXAFS) analysis can confirm that Cs+ bound to illite is coordinated with the outer surface (O-OS) and interlayer surface oxygens (O-IS) through FES or interlayer sites. Through these processes, Cs+ is adsorbed selectively onto FES, while Cs+ can subsequently move into the interlayer and become more strongly fixed.