Microbes have co-evolved with other organisms for eons, to the extent that some are so acquainted with host cell biology that they subvert key cellular processes with unrivalled precision. Pathogenic bacteria and viruses, for example, are extremely adept at intercepting host signal transduction pathways, re-routing protein traffic, remodelling the cytoskeleton and influencing host cell differentiation or death. Symbionts and commensal organisms, too, have evolved sophisticated strategies to derive benefit from the host environment without eliciting responses that compromise their viability. This volume reviews this exciting new discipline, reflecting both the recent explosion of knowledge and the wider insights into fundamental cellular processes that are provided. The authors, chosen for their contributions to the field, cover all the salient aspects using a range of model systems.