Abstract
Our gut harbors more microbes than any other body site, and accumulating evidence suggests that these organisms have a sizable impact on human health. Though efforts to classify the metabolic activities that define this microbial community have transformed the way we think about health and disease, our knowledge of gut microbially produced small molecules and their effects on host biology remains in its infancy. This Outlook surveys a range of approaches, hurdles, and advances in defining the chemical repertoire of the gut microbiota, drawing on examples with particularly strong links to human health. Progress toward understanding and manipulating this chemical language is being made with diverse chemical and biological expertise and could hold the key for combatting certain human diseases.