Enterococcal species, though most commonly regarded as members of the microbial flora of the intestinal tract, have recently emerged as human pathogens of significant concern. The rapid spread of antibiotic resistance among enterococci, which has resulted in strains now being routinely isolated that are resistant to all bactericidal regimens, has prompted considerable interest in investigating the pathogenesis of enterococcal infection, with a view toward deriving new, information-based treatment strategies. This review summarizes major findings on the pathogenesis of enterococcal infection, fits them into a model for the dual lifestyle of enterococci as commensal and pathogen, and integrates into that model a recently discovered pathogenicity island of Enterococcus faecalis.