Many ectothermic species are currently expanding their geographic rangepolewards, which makes for exciting natural evolutionary experiments and offers unique opportunities to study evolutionary processes related tospecies ranges. The factors that ultimately determine range sizes, range limits and their dynamics are key issues in ecology and evolution. Inthis study we aimed to shed a light on the drivers of range size acrossthe different species of the damselfly genus Coenagrion. Starting from this framework the genetic signature of the current poleward range expansion of one Coenagrion species, C. scitulum was assessed at different spatial scales.The integrated macroecological and macroevolutionary analysis of potential drivers shaping variation in species range size in Coenagrion damselflies identified two ecological contributors: species range sizes were larger in northern areas and larger in species with a higher dispersal capacity. The genus Coenagrion invaded the Nearctic twiceindependently from Eurasia, yet this was not associated with the evolution of larger range sizes or higher dispersal.Thirteen microsatellite markers for Coenagrion scitulum were developed, which were used to unravel the genetic structure of C. scitulum and microevolutionary consequences of range expansion. The genetic structure of C. scitulum was found to be shaped by both historical (rapid postglacial range expansion) and contemporary processes (environmental factors and current range expansion). The phylogeographic context, particularly the knowledge about historical colonisation processes, proved to be essential in understanding andidentifying the genetic signatures of local contemporary processes.In C. scitulum edge populations are situated in different directions of a broad expansion front which allowed investigating the genetic consequences using replicated edgepopulations along directions other than the North-South direction, thereby avoiding potential confounding effects of latitude. Using both microsatellite markers and SNPs we documented that a range expansion along multiple axes is associated with a reduction in genetic diversity and stronger genetic differentiation in the edge versus the core populations, suggesting founder effects during range expansion. The persistence of these neutral genetic signatures was assessed in a spatiotemporal study along one particular axis. We showed that the genetic structure changes in time due to genetic immigration and admixture from a broad expansion front.Besides the study of neutral genetic patterns, we also screened for genomic changes associated with the documented phenotypic differentiation due to range expansion. A large set of SNPs was used to screen for putative loci associated with range expansion and thermal regimes. Only a very small portion of the sequenced genomewas associated with range expansion per se, suggesting either limited evolutionary changes or evolution through independent molecular pathways,likely involving traits with a polygenic nature. Nevertheless, one SNP under selection due to range expansion per se was detected and moreover was found to be associated with dispersal capacity. A second SNP was associated with adult flight period temperature and phenotypic traits linked to temperature regulation. These results demonstrate the added value of phenotypic data to the genome-wide scan for selection.The results of this thesis highlight the possibility of fast microevolutionary changes, which on their turn could affect further ecological changes. We should hence continue to study species ranges at the ecological and evolutionary level as both shape their dynamics. With the knowledge gained in this study, a next step would be to genetically analyse neutral genetic variation and the regions around the detected SNPs in new populations at the different expansion axes that are likely to be established in the future. This would allow tostudy the still largely unexplored evolutionary processes associated with range expansion in real-time.