The twentieth century has seen the emergence of chemotherapy, which has represented one of the most powerful tools to fight pathogenic agents as various as bacteria, fungi and protozoan or metazoan parasites both in the field of human and veterinary medicine. However, at the beginning of this new century, it is obvious that chemical treatments are now facing limitations. The case of gastrointestinal nematode of ruminants (GIN), has been chosen as an illustration of this novel situation and consequently, the enforced “evolution” in methods of disease control. Gastrointestinal parasitism remains a main pathological constraint associated with the breeding of ruminants. The usual mode of control of these diseases is represented by the repeated use of anthelmintics (AH) to maintain parasitism under a level that does not penalise animal health and welfare and comprises with objectives of production. However, this quasi exclusive reliance on chemotherapy is nowadays strongly questioned by the constant and widespread diffusion of AH resistance in nematode populations. The increasing concern of consumers on the use of chemicals in farm industry and for animal welfare has also been considered since it leads to a strengthened regulation on the use of treatments in farm animals and to a renewed interest for less intensive systems of production, such as organic farming. These various reasons explain the current demand for alternative methods to complement or replace chemotherapy. Such methods can be classified according to 3 principles.