In order to be successful, a plant pathogen must be able to tolerate the host environment, evade or overcome preformed defenses and suppress or fail to elicit induced defenses. Components such as lipopolysaccharides, peptidoglycan, chitin, and glucan are considered to be microbe-associated molecular patterns, molecules that comprise (relatively) invariant structural moieties and that are indispensable to the pathogen, but which are recognized by plants to elicit defense responses. In phytopathogenic bacteria, extracellular polysaccharides and extracellular cyclic glucan have been implicated in suppression of particular defense responses. It is evident that microbial glycosylated components can play important, and sometimes opposing, roles in plant-microbe interactions. Roles such as elicitation of plant defenses are of benefit to the host. Conversely, other roles such as promotion of colonization of plant surfaces, suppression of basal defense responses and increasing microbial tolerance to the host environment, are of benefit to the pathogen. Bacterial polysaccharides can also have additional roles in other aspects of pathogen behavior that may include colonization of plant surfaces, biofilm formation, and tolerance to the host environment.