Volcanic threat is a combination of destructive natural phenomena that a volcano is capable of producing (volcano hazard) and the people, property, and infrastructure at risk from these phenomena (exposure). Matching a volcano’s required monitoring level to its threat level provides the most safety for the most people and infrastructure at risk, and it most efficiently distributes funds and scientists’ time. Matching required monitoring to threat level became possible in 2005 when the USGS quantified volcano hazard, risk exposure, and threat levels for all 169 geologically active volcanoes in the United States and its territories (Ewert et al., 2005).