The mechanisms of adsorption of hydrogen on the anatase TiO 2(101) surface and of its diffusion in the bulk are investigated with DFT calculations and compared with similar results obtained for the diffusion of hydrogen on the rutile (110) surface. Because of the different oxygen environments in anatase and rutile surfaces, the H binding energy on the anatase surface is 0.2-0.3 eV smaller than in rutile. Various processes for H diffusion are investigated using the climbing nudged-elastic-band (cNEB) approach. We have identified three main diffusion mechanisms, leading to migration of H on the surface, diffusion into the bulk, and desorption of H2 molecule. Our calculated activation barrier (Eact) shows that migration of H into the bulk is the kinetically most favorable process. © 2011 American Chemical Society.