[en] Magnetite is a material used for catalysts in some of today's most important industrial processes, the Haber-Bosch and Fischer-Tropsch processes. It has raised attention due to its catalytic behaviour in the water-gas shift reaction, its potential use in spintronic devices and hierarchical materials. There are however still a lot of open questions concerning these potential applications, because the mechanisms at the surface that play an important role in these are not fully understood. The structure of the √(2) x √(2)R 45 ° reconstruction that forms on the clean magnetite (001) upon preparation in ultra-high vacuum, which was formerly explained by a bulk-truncated model, had to be revised due to new observations that were unexplainable with the former model and led to the proposition of a new model. This was also invalidating former interpretations of lifting processes of this reconstruction due to significant differences between the models. To solve some of these open questions, surface X-ray diffraction measurements have been performed on the (001) surface of magnetite exposed to several different conditions. Following the surface science approach, the first system investigated was the structure of the clean, reconstructed surface to revalidate the newly proposed structural model as a bare for all of the following experiments. Due to an excellent agreement with the surface X-ray diffraction data measured on this surface, the new, non-stoichiometric structural model was confirmed. A further structural refinement was performed, but only led to some minor changes in the model. In addition, the impact of certain features of the model on the data was investigated by simulations to get a better understanding on the sensitivity of the measurements for these. Based on this, the structural changes in the surface upon dissociative adsorption of formic acid was investigated. The formate that forms during this process and adsorbs on the surface is a proposed intermediate in the water-gas shift reaction, and acts as a probe molecule for the interaction of other carboxylic acids with the surface. Dosing formic acid was known to lift the √(2) x √(2)R 45 ° reconstruction of the surface, and, following a structural analysis of the obtained diffraction data of this surface, it could be shown for the first time that the surface changes back to bulk-stoichiometry, involving the reorganisation of iron cations at the surface as well as iron diffusion from lower layers towards the surface. A full structural refinement was performed, and the resulting model agreed well with the adsorption geometry proposed in literature. In addition, water vapor and atomic hydrogen, both also known to lift the surface reconstruction at room temperature, were also dosed on the clean reconstructed surface and its structure investigated. The pressure region in which water vapor lifts the reconstruction was found to be between 1 x 10^-4 mbar and 1 x 10^-3 mbar, which agrees nicely with the reported onset of hydroxylation of the surface reported in literature. Both water vapor and atomic hydrogen were found to not only completely lift the reconstruction, but also lead to an atomic roughening of the surface within the first two layers. For atomic hydrogen, this was also confirmed by Scanning-Tunneling Microscopy measurements. This indicates significant iron diffusion and, subsequently, a surprisingly high mobility of iron cations at the surface under these conditions. No different phase was formed at the surface, and the analysis indicates ordered hydroxyl to be present at the surface during water dosing as well as after pumping back down. To complement the X-ray diffraction measurements, X-ray photoelectron spectroscopy measurements were performed before and after dosing of formic acid, water vapor and atomic hydrogen. A rather large amount of carbon was found to bc present on the surface after water vapor dosing. The same observation was made upon exposure to atomic hydrogen, but in contrast to the water vapor exposed surface, the amount of carbon increased even further over time. This indicates that the hydroxylated surface is attracting carbon from the residual gas even under ultra-high vacuum conditions. Finally the reversible lifting of the surface reconstruction upon heating was investigated. The resulting data from the Lifting process agreed well to what was described in literature. The cause of this was found to be a decrease in the long-range ordering at the surface due to diffusion of iron at the surface, exhibiting a fundamentally different lifting mechanism than what was found under the previous conditions.