In Holland a PhD research at Wageningen University & Research shows that genetic selection of animals to make them less susceptible to infections is an interesting intervention. The current approach in animal breeding to select for lower infection susceptibility, however, purely focusses on the individual animal, ignoring the fact that infections are transmitted from animal to animal in populations. This thesis shows that by ignoring the transmission of infections, breeders miss a considerable part of the heritable variation. Thereby, the potential of genetic selection to reduce the impact of infectious diseases in livestock populations is much larger than always thought.