The structure of coastal dunes from three different sites within Wales, UK, have been investigated using ground penetrating radar (GPR), revealing the internal structure of the dunes. GPR provides a unique insight into the internal structure of coastal dunes that cannot be achieved by any other non-destructive or geophysical technique. The profiles presented show results from surveys investigating sand thickness and distribution, and dune structure and statigraphy. Surveys at Towyn Warren map the base of the sands with their structure interpreted as a transgressive sand sheet that wedges out towards the North. Surveys at The Bennet reveal a complex internal structure of prograding units and cross-cutting erosion surfaces allowing the construction of a relative chronology for the dune. Profiles from Freshwater reveal sets of sedimentary structures including cross- stratification, dipping foresets, cut and fill troughs, bounding surfaces and erosion surfaces. These structures are interpreted in terms of the dunes evolution allowing the identification of periods of accretion and progradation, erosion, re-working, stabilization and major events in the dunes history. The water table is resolved, and the effect of saline waters on attenuation is shown.