Aphids are the one of the most serious pest insects in crops around the world. They penetrate the plant tissue with their stylets and feed from the phloem vessels. Their infestation causes economic losses by negatively affecting crop growth, development and quality of the harvested product, as well as by transmitting viruses. To control aphid population growth in crops, using aphid resistant varieties may be a sustainable and environmentally friendly strategy. The green peach aphid, Myzus persicae, is an economically important pest of cultivated pepper plants (Capsicum). Unfortunately, there is no pepper variety resistant against M. persicae and no sources of aphid resistance have been used in pepper breeding so far. The aim of this PhD-thesis was to obtain more knowledge about aphid resistance in pepper and the pepper-aphid interaction, including identification of new sources of resistance against M. persicae, elucidation of resistance mechanisms, identification of Quantitative Trait Loci (QTLs) functioning in aphid resistance and exploration of the virulence mechanism of M. persicae on pepper.