Over the past fifty years cells and mediators involved in our immune defences have been painstakingly identified. However, it is only relatively recently that the ability of microorganisms to evade immunity has been recognized and investigated. This volume introduces the mechanisms used by bacteria to evade both humoral and cellular immune responses, using systems ranging in complexity from the simple quorum sensing molecules (acyl homoserine lactones) to the supramolecular syringe-like devices of type III secretion systems.