Significant progress has been made recently in the molecular epidemiology of rickettsial diseases. This presentation will review molecular approaches for assessing the dynamics and transmission of rickettsial agents, identification of the origins of outbreaks of rickettsioses, and identification and characterization of new rickettsial pathogens. Special emphasis is given to novel SFG rickettsioses in the Americas, and particularly in California. The impact of continuously growing list of new rickettsial pathogens on public health including contemporary disease surveillance, diagnosis, prevention, and control of rickettsial diseases will be discussed.