lthough we often think of evolution and ecology in strictly macroscopic terms, the forces of environment, natural selection, and population dynamics operate if anything even more purely in the microscopic realm of bacteria, viruses, and parasites. The interactions between these microbes and their macroscopic plant and animal hosts -- particularly how those interactions relate to issues of pathogenesis, symbiosis, and the role of selection, and how the emerging science of microbial genomics can cast light on those issues -- forms the topic of Science's Special Issue of 11 May 2001.

To provide some context for the articles in this Special Issue, we've compiled this Web supplement. Included is a selection of classic reviews and articles on related topics published in Science over the past decade, and some worthwhile Web resources providing background and avenues for further investigation.