Coxiella burnetii, the causative agent of Q fever, is a Gram negative coccobacillus. It resides and replicates in the host s monocytes and macrophages. The developmental cycle of C. burnetii includes macrocellular and microcellular forms and the formation of spore-like bodies. It undergoes a phase variation of outer cell surface antigens from virulent phase I to avirulent phase II after passaging in the yolk sac of embryonated chicken eggs or in cell cultures. C. burnetii belongs to the most resistant bacteria. The main reservoirs of C. burnetii are cattle, sheep and goats. Human Q fever usually results from inhalation of contaminated aerosols. Acute infection mostly takes the course of a flu-like disease, atypical pneumonia or hepatitis, the chronic form resembles endocarditis. Laboratory examinations are based on the presence of antibodies. The drugs of choice are broad-spectrum antibiotics.