Anthrax lethal toxin is a multi-functional virulence factor that has evolved to target multiple host functions to allow for optimal establishment of Bacillus anthracis infection. The toxin appears to play a role in all stages of infection, from germination to the induction of vascular collapse leading to host death. Early in infection, at sublethal doses, it acts to suppress immune cell and cytokine responses, thereby promoting bacterial outgrowth. Later in the disease, lethal levels of toxin induce the cytokine-independent shock-like death associated with anthrax. The understanding of the molecular events induced by anthrax toxin in different target cells at each stage of infection will aid in deciphering the pathogenesis of this bacterium and developing therapies.