A little more than a decade ago, the southern midcontinent of the U.S. began experiencing an increasing number of earthquakes, including several large events in Arkansas and then Oklahoma. As that increase in seismicity spread to multiple states, attention focused on how disposal of large volumes of brine from oil production could trigger earthquakes. This volume examines that phenomenon in Arkansas, Oklahoma, Texas, Kansas, Colorado, and New Mexico, and details the regulatory response to it, providing a case study in dealing with an unexpected natural resource hazard.