Viruses must infect cells to complete the intracellular phase of their life cycle. They have evolved a broad palette of ingenious mechanisms to exploit host cell biology, using the host's metabolic and regulatory pathways to facilitate their proliferation while providing a niche to evade immune detection. A number of parasitic bacteria and eukaryotes have evolved similar strategies. Understanding the cellular mechanisms targeted by microorganisms is essential to achieving therapeutic in-roads against diseases ranging from global epidemics, such as AIDS and malaria, to persistent public health problems, such as Salmonella and Chlamydia infections.

The concept of targeting host pathways co-opted by a microorganism—as yet underexploited—may allow for the development of more effective antimicrobials that are not subject to the emergence of drug resistance due to mutation of the evolutionary less constrained microbial drug targets. Since the biology of commensal microorganisms, which live in symbiotic harmony with their host and play important roles in its metabolism and immune modulation, overlaps with that of pathogenic microorganisms, therapeutic intervention must consider these side effects.

The study of cellular pathways used by microorganisms has yielded many insights into eukaryotic biology; for example, studies of retroviruses laid the foundation for molecular cancer research thirty-three years ago (marked by the 1989 Nobel prize). To take stock of this rapidly progressing field, NCB has teamed up with Nature Reviews Microbiology to commission a series of seven review articles entitled 'Microbial host cell subversion'. With a topic of such breadth, the aim is not to provide an encyclopaedic overview, but rather an in-depth analysis of cutting edge research on selected topics that exemplify key concepts.

In this journal, Mercer and Helenius review a new key mode of viral entry, macropinocytosis, and Randow and Lehner provide an overview of how viruses make use of their host's ubiquitin system to evade immune responses. Brodsky and Medzhitov compare acute and persistent pathogens, and how they respectively disrupt or manipulate the host immune signalling pathways.

In Nature Reviews Microbiology, Tang and colleagues review how certain bacteria are able to reside in the host cell cytosol where they obtain nutrients for growth and avoid host immune responses. Grinstein and colleagues discuss how bacteria enter host cells through phagocytosis and the mechanisms that they use to counteract host cell defences, and Lora Hooper asks how the commensal bacteria that form the all important gut flora interact with intestinal epithelia to maintain a stable niche. Tilley and colleagues review the remodelling of host red blood cells triggered by the more than one hundred known secreted effectors of malaria parasites.

An accompanying web focus draws together relevant recent primary and review papers from across the Nature family of journals. We hope this collection will stimulate microbiologists and cell biologists alike to engage in collaborative projects to expand our understanding of how microbes and host cells interact. Apart from the intellectual excitement of mapping complex interactions across the phylogenetic tree, such research continues to have important health and biotechnology implications.