Primary research focus is the human indigenous microbiota (microbiome), and in particular, the nature and mechanisms of variation in patterns of microbial diversity within the human body as a function of time (microbial succession), space (biogeography within the host landscape), and in response to perturbation, e.g., antibiotics (community robustness and resilience). One of the goals of this work is to define the role of the human microbiome in health and disease. We are particularly interested in measuring and understanding resilience in the human microbial ecosystem. Our work includes the human oral cavity, gut, and female reproductive tract, as well as an analysis of microbial diversity in marine mammals. This research integrates theory and methods from ecology, population biology, environmental microbiology, genomics and clinical medicine.