Abstract：A growing body of evidence in the 20th century led to the realization that inhalation of asbestos-bearing dusts was the cause of several serious respiratory diseases (asbestosis, lung cancer, and mesothelioma) among workers of asbestos-related occupations, such as asbestos mining, shipbuilding, and asbestos product fabrication. As a result, a number of regulations were developed to govern asbestos dust exposures in specific manufacturing, mining, and other occupational sites. Less straightforward is the regulation and management of “naturally occurring asbestos” (NOA), which has recently gained the attention of regulatory agencies, health agencies, and citizen groups. NOA includes minerals described as asbestos that are found in-place in their natural state, such as in bedrock or soils. NOA is of concern due to potential exposures to microscopic fibers that can become airborne if asbestos-bearing rocks are disturbed by natural erosion or human activities (road building, urban excavations, agriculture, mining, crushing, and milling, as just a few examples). Natural asbestos deposits range widely in size, from thin, scattered veinlets to large ore bodies. Their geographic distribution is directly linked to geology. The geologic settings in which asbestos occur are Mg-rich host rocks altered by relatively low pressure and temperature metamorphism. Specifically, the rock types known to host asbestos include metamorphosed and metasomatized ultramafic rocks (particularly serpentinite) and some mafic igneous rocks, metadolostones, and metamorphosed iron formations. Asbestiform amphiboles can also occur as accessory minerals in several hydrothermally altered types of alkaline igneous intrusions.Recognizing that asbestos forms in predictable and identifiable geologic environments is information that allows public health agencies to conduct an informed asbestos screening and management program. The first steps involve locating and describing the known (reported) asbestos deposits, at a regional or national scale. Next, the geologic units that host known asbestos are mapped, which delineates the extent of possible additional asbestos mineralization. This geological approach allows agencies to plan for the possibility of encountering asbestos where appropriate, while also sparing the unneeded expense of asbestos regulation in regions that are unlikely to contain asbestos deposits. A basic understanding of the geology of asbestos can be applied beforehand at any rock and soil excavation project, regardless of scale. This scientific approach to asbestos management will help alleviate the need to continually respond to surprise discoveries of natural asbestos deposits uncovered by excavation projects. Thus, by mapping the terrains most likely to host asbestos mineral deposits, planners can develop dust-control procedures appropriate for the regions where workers and nearby residents are most likely to be exposed to airborne asbestos.