The hydrologic community lost one of its most charismatic leaders with the death of Paul Witherspoon on 10 February 2012, in Berkeley, Calif. He passed away from complications brought on by his long battle with Parkinson's disease. He was 93. Paul was a dynamic and influential research leader in hydrogeology for more than 50 years. Working from his base at the University of California, Berkeley (UC Berkeley), and later from the Lawrence Berkeley National Laboratory (LBNL), he made significant contributions to the understanding of the flow of fluids in porous media and fractured rock, and he applied his findings to a diverse set of societally important issues, including the development of geothermal energy, use of underground gas storage, and siting and design of nuclear waste disposal facilities. In all these spheres of interest he emphasized the need to marry theoretical studies and field testing. He was especially passionate about the need for large-scale, in situ, underground experiments to guide and corroborate the predictions of theoretically based numerical models.