First principles investigation of hydrogen interaction with metals Zusammenfassung: The presence of hydrogen (H) in metals has a deleterious effect on their mechanical properties. This phenomenon is called hydrogen embrittlement (HE). Since the susceptibility of a metal to HE is strongly dependent on the rate and mode at which H can accumulate at a location of embrittlement the transport of H is a critical aspect of HE. This thesis aims to advance the understanding of H trapping and diffusion in the microstructure of materials by means of first principles methods. As first step we considered the diffusion of H in bulk metals. The diffusion coefficients of interstitial hydrogen in bulk Fe and Ni crystals have been calculated over a wide range of temperatures. Quantum mechanical effects have been included using the semi classical transition state theory (SC TST) and the small polaron model of Flynn and Stoneham. Our results show that it is crucial to include such effects for a quantitative simulation of diffusion of H in bcc Fe even at room temperature while in case of H in fcc Ni this is less important.Then we investigated the interaction of H interstitial with Ni grain boundaries and with TiC precipitates in Fe. In the former case two distinct types of GBs have been considered: the U+03A3 3(111)[ 110] with a close packed atomic interface structure and the U+03A3 5(210)[001] with a less dense structure consisting of open structural units of atoms. Our calculations reveal that these two GBs have markedly different interaction behaviors with interstitial hydrogen atoms