Nematodes are among the most serious threats to livestock. They cause disease and death but they also compromise production. Even a mild infection can cause a relative protein deficiency and reduce weight gain by 25% . In the UK sheep industry alone, nematode infection costs over 100 million Euros a year .The mainstay of current control measures is anthelmintic treatment but this is threatened by the evolution of drug resistance in parasite populations. Alternative or supplementary control measures are urgently needed. The most promising option for control of nematodes is exploitation of genetic variation which is cheap, surprisingly rapid and has proved to be successful in Australia and New Zealand. There are two obstacles to exploiting genetic variation in resistance to nematodes. Many farmers lack expertise in breeding for disease resistance; simplified breeding strategies that utilise markers for disease resistance will help here. Also, there are concerns about sustainability of breeding for resistance to nematodes.A systems biology approach is necessary in order to develop the comprehensive understanding necessary to simplify breeding to ensure that disease control is likely to be sustainable. A systems approach will also help to identify the most suitable combination of approaches under different circumstances. Systems biology combines a variety of disciplines in a quantitative way to achieve a coherent, consistent and comprehensive understanding of host-parasite relationships.This project aims to identify markers for host resistance to nematodes and to enhance our understanding of the host-parasite interaction. We will train a cadre of researchers with the necessary skills to apply quantitative approaches to parasitology and with the essential experience to apply this knowledge to the livestock sector.