Scientific American's Katherine Harmon reports on how epidemiologists, inspired by the impact of hard data generated in genomics research, seek to develop a "detailed map of environmental exposures that might occur throughout a lifetime, which can be mapped onto the etiology ... of major illnesses, including cancer, diabetes and heart disease," or an "exposome." Steve Rappaport at the University of California, Berkeley, tells Scientific American that researchers "really need to think about the environment as what's going on inside the body and accept things that come from every source." In an editorial appearing in this week's Science, Rappaport and Martyn Smith, also at Berkeley, make a case for mapping the exposome; they suggest that "successful characterization of both exposomes and genomes, environmental and genetic determinants of chronic diseases can be united in high-resolution studies that examine gene-environment interactions" and, further, that "such a union might even push the nature-versus-nurture debate toward resolution."