In this chapter, hydrogen (H) kineticsKinetics in metals are schematically described with the separation of absorptionAbsorption, desorptionDesorption, diffusion, permeationPermeation and trappingTrapping, and what are derived from these experiments. Literatures on H interaction with metals have been focusing to diffusion, permeation, and trapping to derive apparent diffusivity, permeabilityPermeability, and evaluate trappingTrapping parameters such as trap density, trapping or detrappingDetrapping energyDetrapping energy. These parameters are useful to reproduce individual experimental results. However, all are for transient phenomena in a rather short period, while long-term changes of trapping for example are seldomly observed. The depthProfiling profilingDepth profile clearly indicates that the appearance of H trapping is not simple but changes significantly depending on the amount of dissolved HDissolved H. Therefore, without knowing the depth profilesDepth profile, overall H behavior analyzed by TDSThermal Desorption Spectroscopy (TDS), for example, could lead to misinterpretation of the H kineticsKinetics. That means it is critically important to know the mechanism of trapping and detraping in near atomic scale. In addition, large difference in H chemical potentialChemical potential of outside and inside of a H loaded metal after the loading should force H profilesH profile change. Therefore, it is quite important to know sequential changesSequential change ofH concentration H concentrationConcentration profilesConcentration profile not only for the large scale but also microscale around trapping sitesTrapping site.