As a group, rickettsiae, and related bacteria, contain a number of human pathogens that have recently named as causes of `emerging diseases'. This unique volume offers a thorough and current review of information on the pathogenesis and immune response elicited by memebers of the genera Rickettsia, Ehrlichia, Coxiella, Orlentia, and Bartonella, in contributions authored by the expert clinicians and researchers who work with these organisms.