“Fiber Optic Distributed Sensing as a Window on Subsurface Flow” The advancement of fiber optic distributed sensing over the past two decades has enabled the measurement of subsurface hydraulics and geomechanics at unprecedented temporal and spatial detail. We will look at how this technology has improved our understanding of subsurface flow related to diverse applications such as stream discharge, managed aquifer recharge, remediation of contaminated sites, aquifer testing, fracture hydromechanics, and energy resources.