Earth science has long benefited from methods and technology developed in other fields of science and medicine. Medical imaging technologies such as X-ray computed tomography (X-ray CT) and positron emission tomography (PET), are invaluable tools for expanding our understanding of continuum-scale subsurface flow processes. My PhD work focused on using PET imaging techniques combined with numerical and analytical methods to better understand transport processes such as spontaneous imbibition in heterogeneous geologic porous media, solute transport in vesicular basalt, and dispersion in heterogeneous systems during single and multiphase flow. In my current position at Imperial College I am utilizing the world-class micro-computed tomography imaging capabilities to experimentally observe many of these same processes at the pore scale. Understanding the fundamental physics of these systems has a number of important applications in hydrogeology, reservoir engineering, and environmental science, such as improving confidence in the long term storage security of geologically stored carbon dioxide, addressing non-aqueous phase groundwater contamination, and saltwater intrusion. Outside of earth and environmental science, understanding these fundamental mechanisms of transport in porous media also has important applications in fuel cell design, dendrology, and paper and textile manufacturing.