Part I. Evolutionary Biology of Animal Host-Bacteria Interactions: 1. How have bacteria contributed to the evolution of multicellular animals? Carol Hickman; 2. The interface of microbiology and immunology: a comparative analysis of the animal kingdom Margaret McFall-Ngai; 3. Co-evolution of bacteria and their hosts: a marriage made in heaven or hell? Jörg Hacker, Ulrich Dobrindt, Michael Steinert, Hilde Merkert and Ute Hentschel; 4. Industrial revolution and microbial evolution Fernando de la Cruz and Julian Davies; 5. Bacteria evolve and function within communities: observations from experimental Pseudomonas populations Paul B. Rainey; Part II. Bacterial Ecology and the Host as an Environment: 6. Coral symbioses: the best and worst of three kingdoms Eugene Rosenberg; 7. Interactions between inherited bacteria and their hosts: the Wolbachia paradigm Zoe L. Veneti, Max Reuter, Horacio Montenegro, Emily A. Hornett, Sylvain Charlat and Gregory D. Hurst; 8. Microbial communities in lepidopteran guts: from models to metagenomics Jo Handelsman, Courtney J. Robinson and Kenneth B. Raffa; 9. Commensal diversity and the immune system: modelling the 'host-as-network' Robert M. Seymour; Part III. Cellular Interactions at the Bacteria-Host Interface: 10. Beneficial intracellular bacteria in the Dryophthoridae: evolutionary and immunological features of a pathogenic-like relationship Abdelaziz Heddi and Caroline Anselme; 11. Regulation of Bordetella-host interactions: mechanisms and evolution Seema Mattoo and Jeff F. Miller; 12. Resident bacteria as inductive signals in mammalian gut development Lora V. Hooper; 13. Virulence or commensalism: lessons from the urinary tract Göran Bergsten, Björn Wullt and Catharina Svanborg; Part IV. Bacterial Interactions with the Immune System: 14. Host responses to bacteria: innate immunity in invertebrates L. Courtney Smith; 15. Bacterial recognition by mammalian cells Clare E. Bryant and Sabine Tötemeyer; 16. Moonlighting in protein hyperspace: shared moonlighting proteins and bacteria-host crosstalk Brian Henderson; 17. Cell signalling pathways as targets for bacterial evasion and immunity Andrew N. Neish; 18. Shaping the bacterial world by human intervention Rino Rappuoli.