Although many plant pathogens are known for their capacity to develop resistance to classical control methods, only few studies have explored their ability to overcome the effect of biocontrol agents. However, these studies highlight differences in the sensitivity of various isolates of plant pathogens to biocontrol agents or to compounds that are produced or synthesized as the result of their interaction with the host-plant. This observed diversity may contribute to the inconsistent efficacy of biocontrol agents sometimes observed in the field. Moreover the selection pressure exerted by an increase in the use of biocontrol agents may cause the emergence of new resistant phenotypes from these less sensitive isolates. This review highlights current knowledge concerning erosion of biocontrol against plant pathogens and its possible consequences for field efficacy.