Intracellular pathogens are responsible for a number of important diseases worldwide, including tuberculosis, plague and bacillary dysentery. This volume focusses on those intracellular pathogens that have been studied most extensively at the molecular, genetic, and cellular level. The reviews attempt to integrate the information derived from these diverse approaches into a cohesive picture. In recent years the entry steps have been described at the molecular and genetic level, and the important signal transduction events are being elucidated. It is now becoming clear that there are both similarities and differences both in terms of the steps involved and of the genetic basis of bacterial invasiveness. These reviews of the state of the art provide a foundation from which to proceed.