The study of sediment dynamics within the Seine estuary and its adjacent shelf permits some conclusions regarding sediment exchanges in this coastal zone. On the shelf, sediment transport is directed toward the Seine estuary and contributes to the infilling of the estuary by marine sands and muds; these were originally derived from land carried to the shelf at times of lower sea level, and subsequently transported shoreward by dominant tidal and wave-induced currents. In the estuarine section, tidal processes form a turbidity maximum both by inducing strong bed resuspension and by trapping fluvial and marine sediments due to flood current predominance. Occasionally this turbid zone extends seaward during periods of river floods, and sediment is redispersed onto the shelf. This phenomenon has been amplified by man-made modifications of the estuarine morphology. However, currents patterns tend to retard the natural seaward escape of fluvial material, mainly due to dredging operations at the present time. Thus, man has changed the natural role of the estuary from a sink to a source of fluvial sediments for the shelf. A tentative sedimentary budget is proposed, taking into account the various sources of material and the complexity of sediment dynamics.