Polyamines are polycationic molecules with a hydrocarbon backbone and multiple amino groups. Descriptions of the physiological roles of polyamines have often been limited to their interaction with negatively charged nucleic acids. Of late, reports linking polyamines to microbial carcinogenesis, biofilm formation, escape from phagolysosomes, bacteriocin production, toxin activity and protection from oxidative and acid stress have been published, providing insights about their other important but lesser known functions. This review focuses on recently discovered novel functions of polyamines in microorganisms, with an emphasis on bacterial pathogens of humans.