The study investigates the biogeography of bacterial communities on the human body, aiming to establish healthy baselines for detecting differences associated with diseases. Researchers surveyed bacteria from 27 sites in 7–9 healthy adults on four occasions, using a multiplexed barcoded pyrosequencing approach. They found that community composition was primarily determined by body habitat, with high interpersonal variability within habitats and minimal temporal variability. Skin locations harbored more diverse communities than the gut and mouth, and skin sites showed different community assembly patterns. The results indicate that the human microbiota varies systematically across body habitats and time, which may help understand how microbiome changes cause or prevent diseases. The study also highlights the need to specify body habitats in microbial surveillance studies and to consider local conditions to understand resistance to microbial invasion.The study investigates the biogeography of bacterial communities on the human body, aiming to establish healthy baselines for detecting differences associated with diseases. Researchers surveyed bacteria from 27 sites in 7–9 healthy adults on four occasions, using a multiplexed barcoded pyrosequencing approach. They found that community composition was primarily determined by body habitat, with high interpersonal variability within habitats and minimal temporal variability. Skin locations harbored more diverse communities than the gut and mouth, and skin sites showed different community assembly patterns. The results indicate that the human microbiota varies systematically across body habitats and time, which may help understand how microbiome changes cause or prevent diseases. The study also highlights the need to specify body habitats in microbial surveillance studies and to consider local conditions to understand resistance to microbial invasion.