For the ground-penetrating radar (GPR) method in reflection mode, a broadband electromagnetic (EM) wave is generated at the surface.  This wave then propagates through the earth and is reflected at boundaries separating materials with contrasting electromagnetic properties.  The reflected waves are recorded at the surface and used to produce an image of the subsurface that is similar to a cross-section of the earth.  This method is useful for measuring the geometry of stratigraphic units in lithologic settings with low electric conductivity such as sand dominated aquifers.  To a large extent, the propagation of EM waves in shallow groundwater systems is controlled by the volumetric water content.  This is due to the large contrast in dielectric permittivity between water (K~80) and the rock matrix (K~4).  If we properly acquire and process GPR data, we can take advantage of this large property contrast to estimate the moisture content of the subsurface.  Using the established geometries developed in seismic exploration, multi-fold, common-midpoint GPR acquisition gives rise to improved subsurface characterization through three key features: 1) Processes such as stacking and velocity filtering significantly attenuate coherent and random noise resulting in subsurface images that are easier to interpret, 2) multi-fold data enable measurement of vertical and lateral velocity variations which lead to improved understanding of material distribution and more accurate depth estimates, and 3) multi-fold data enable observation of reflected wave behavior at a common reflection point for various travel paths through the subsurface - quantifying these variations can be a valuable tool in material property characterization.  Recent development of commercial multi-channel GPR systems makes multi-fold acquisition a feasible option for many applications.  Using modeling, laboratory, and field examples, I demonstrate how GPR methods can improve our understanding of shallow groundwater systems through detailed measurement of electric properties and improved subsurface images.