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In this thesis I studied plant-soil interactions of range-expanding plant species: plants that have expanded their range northward due to recent climate change. The interactions of these plant species with associated belowground organisms are predicted to change along their range expansion trajectory, as belowground organisms have limited dispersal capabilities. I show that nematode communities under range-expanding plant species indeed change along a latitudinal transect across Europe, but that range-expanding plant species only rarely experience less herbivory from nematodes in their new range compared to their original range. Greenhouse studies showed that in the new range, the direct and indirect interactions of range-expanding plant species with root-feeding nematodes differ from similar interactions of native plant species, but that the outcomes of such interactions are highly species-specific. The level of dissimilarity in root chemistry between range-expanding plant and related native plant species may determine the responses of native nematodes to range-expanding plant species in their new range. I also show that phylogenetic distance is not a good predictor of variation in plant-soil interactions among native and range-expanding plant species. Overall, my thesis shows that interactions of range-expanding plant species with soil organisms in their new range are species-specific, and that the impact of range-expanding plant species on communities in their new range cannot be easily predicted.