Bacterial pathogens utilize several strategies to modulate the organization of the actin cytoskeleton. Some bacterial toxins catalyze the covalent modification of actin or the Rho GTPases, which are involved in the control of the actin cytoskeleton. Other bacteria produce toxins that act as guanine nucleotide exchange factors or GTPase-activating proteins to modulate the nucleotide state of the Rho GTPases. This latter group of toxins provides a temporal modulation of the actin cytoskeleton. A third group of bacterial toxins act as adenylate cyclases, which directly elevate intracellular cAMP to supra-physiological levels. Each class of toxins gives the bacterial pathogen a selective advantage in modulating host cell resistance to infection.