Giardia intestinalis is the protozoan responsible for giardiosis, a parasitosis characterized by intestinal malabsorption, diarrhea, weight loss and intense abdominal pain in humans and many animals. This disease, which has a recognized impact on public health (prevalence in adult humans ranges from 2 to 7.5% in industrialized countries, and from 12 to 30% in developing countries), can lead to significant nutritional deficiencies, particularly in young individuals. Infection occurs following ingestion of cysts present in contaminated food or water. Cysts are infectious at very low doses, survive for several months in the environment and are resistant to various disinfectants. The growing number of cases of giardiasis linked to drinking water contamination, the significant side-effects of treatment, and the emergence of strains resistant to available drugs, make this disease an increasingly worrying public health problem, requiring the development of alternative treatments. It is now well established that the intestinal microbiota and certain strains of probiotic bacteria play an important role in protecting against certain intestinal pathogens.