The nocardiosis is an infection caused by a bacterial pathogen agent, Nocardia, belonging to the Actinomycetales order. They are Gram-positive, strictly aerobic bacteria. Members of the genus Nocardia are ubiquitous. They are frequently isolated from soil, water, air dusts. The mode of contamination occurs by inhalation or by cutaneous or ocular traumatic lesion. Clinically, nocardiosis is essentially characterized by pulmonary diseases. Others secondary localizations are described, such as in the central nervous system. Nocardia can be responsible for important cutaneous, subcutaneous and lymphocutaneous manifestations. In the same way, some extrapulmonary diseases and spread nocardiosis are more rarely observed. Several factors seem to favour the development of Nocardia. The immunocompromised patients, particularly those with organ transplant and the patients treated with immunosuppressor treatments, offer strong predispositions to this opportunistic disease. The nocardiosis is nevertheless observed in healthy persons. In front of polymorphic and specific-less clinical manifestations, large phenotypic heterogeneity, and resistance profiles to specific antibiotics, a correct diagnosis for Nocardia species is necessary to apply an adequate treatment. The techniques of identification based on the chemotaxonomic analysis and the susceptibility to different inhibitors are efficient for the identification of genus and species. However, because of the slow growth rate of Nocardia, the reading of these tests can require several weeks of incubation. With the intention of the rapid identification of genus and species, the molecular techniques (PCR-RFLP) seem to be efficient. The technique of RAPD allows an efficient molecular typing, which will give a better knowledge concerning transmission, ecological niches and epidemic reservoirs.