Secretory IgA (SIgA) is the predominant class of antibody found in intestinal secretions. Although SIgA's role in protecting the intestinal epithelium from the enteric pathogens and toxins has long been recognized, surprisingly little is known about the molecular mechanisms by which this is achieved. The present review summarizes the current understanding of how SIgA functions to prevent microbial pathogens and toxins from gaining access to the intestinal epithelium. We also discuss recent work from our laboratory examining the interaction of a particular protective monoclonal IgA with Salmonella and propose, based on this work, that SIgA has a previously unrecognized capacity to directly interfere with microbial virulence at mucosal surfaces.