Ninety percent of the cells in the human body are bacteria, and humans may be host to many thousands of different species of bacteria. These striking statistics are part of a new paradigm in microbiology in which bacteria are no longer viewed as disease-causing killers but more as lifelong partners which are often essential for the survival of their host. This book brings together a group of diverse scientists - evolutionary biologists, immunologists, molecular biologists, microbiologists, pathologists and mathematicians - to discuss the evolution and mechanisms of bacteria-host interactions at all levels of complexity. Chapters deal with the evolution of these interactions over the last 60 years (since the introduction of antibiotics) to a period of 3.8 billion years (since the evolution of single-celled life) and discuss bacterial interactions with multicellular life forms from coral reefs to humans. Researchers and graduate students across the life sciences will find this book of interest.