A commercial version of the magnetic resonance sounding (MRS) technique became available in 1996. At that time, ITC research team started to investigate the MRS technique with respect to its appropriateness to groundwater investigations. MRS is the only non-invasive surface geophysical technique with an inherent selectivity to free hydrogen and, therefore, to groundwater. The signal amplitude inversion allows quantifying free water content as a function of depth and signal decay rate inversion characterizes pore size with depth. The technique is limited in its depth investigation capability mainly by the size of its excitation/sensing loop, by the electric conductivity of the media, by the ambient noise level and by the Earth's magnetic field value. Two field cases illustrate MRS applications. A conglomeratic aquifer within metamorphic fractured rock sequence in Portugal shows the MRS response in a low porosity environment and unconsolidated porous aquifer system in the Netherlands, presents an opposite case of high porosity environment.