Worldwide, vascular wilt disease caused by the fungus Verticillium dahliae affects a wide range of economically important crops. As this disease is difficult to control, disease management is highly dependent on plant resistance. The latter can be achieved by impairing those plant genes which are "abused" by the fungus for its own benefits. Impairing these genes (susceptibility genes) may lead to resistance. Little is known about these genes for V. dahliae, therefore this thesis focused on the identification of susceptibility genes in order to facilitate breeding efforts in tomato to obtain resistance to vascular wilt disease.