Despite the broad armory of vaccines, antibiotics and other weapons at our disposal, pathogenic bacteria and fungi continue to present a serious threat to human health. These pathogens have proved very versatile and many are associated with infections of vulnerable individuals, often in hospital settings. Evidence is accumulating that certain Infections, for example, of medical devices, the cystic fibrosis lung, the oral cavity, the GI tract and wounds, are in fact polymicrobial, with more than one microbe involved. To understand diseases and formulate intervention strategies, it is necessary to know the extent of contact and communication between microbes in these mixed infections. It is now emerging that the signals that microbes use to coordinate expression of viruence factors within a species may also be perceived by other microbes in the community. This article addresses such interspecies signaling and examines the consequences of such signaling between bacterial and fungal pathogens for expression of virulence traits.