Interrelationships between coastal sand dune dynamics and prehistoric human activity are explored from three sites along the sandy, high-energy Atlantic coast of County Donegal, NW Ireland. Dunes at these sites yield artifacts and shell middens of Bronze Age to Medieval date. The detailed sedimentary context of shell middens and associated dark-stained occupation horizons and hearths was investigated from exposures within dune faces. Occupation horizons show mixed shells dispersed throughout, and wind-eroded and lagged upper surfaces. Shells located within these horizons are distinguished from those located within unstained sand, which are interpreted as middens formed marginal to semipermanent occupation sites. Sediments immediately overlying midden and hearth sites contain components (including shell fragments and charcoal) derived directly from these anthropogenic layers. The influence of this sediment source, tracked by the presence and abundance of shell and charcoal fragments, decreases rapidly upward. This field evidence suggests that changes in the nature of the land surface (by devegetation, sediment compaction, development of occupation horizons, hearths) may cause temporary changes in subsequent dune sedimentation processes and sediment characteristics. This also suggests that, as well as being difficult to evaluate using conventional geoarchaeological techniques, the sedimentological impact of past human activity in the coastal zone has probably been underestimated.