AB: The concept of disease emergence is not new. It had been elaborated by Charles Nicolle as early as 1930 in his book: "Birth, life and death of infectious diseases" even if the word itself had not been used. The word became into fashion during the 90s and it must be asked whether it corresponds to a clearly defined notion, unanimously accepted, or it is used too often, indeed outside matters. From the study of some existing definitions, one can propose that an emerging disease is a disease of which the true incidence increases in a significant way in a given population from a given area during a given period, in comparison with the current epidemiological situation of the disease. This definition can be used in human diseases as well as plant and animal diseases. Even if emerging diseases are essentially infectious, they can sometimes include other kinds of diseases, like toxic and metabolic diseases. This definition allows to exclude the bias linked to an apparent increase in the incidence, for example following the improvement of the diagnostic methods. Therefore, the true emergence has to be distinguished from the apparent emergence. Mediatic emergence is also a false emergence which depends on the repercussion that give the media of various events linked to human or animal health. To conclude, it is possible to propose some recommendations for the use of the concept of emergence in pathology.