Control of gastrointestinal nematodes of ruminants is based largely on use of anthelmintics combined, where practical, with pasture management. The increasing prevalence of resistance to anthelmintics has led to the search for alternative sustainable control strategies. Here, we consider how nutrition, as a short-term alternative, can influence the host--parasite relationship in ruminants, using gastrointestinal nematode infections of sheep as the model system. Nutrition can affect the ability of the host to cope with the consequences of parasitism and to contain and eventually to overcome parasitism. It can also affect the parasite population through the intake of antiparasitic compounds.