Suspended matter comes into the North Sea from the Atlantic Ocean, from the Channel, rivers, seafloor erosion, coastal erosion, the atmosphere, and from primary production. The contribution of the last source is temporarily large when phytoplankton growth is abundant, but is soon decomposed, mineralized or consumed so that over the year the net effect is small. Accumulation and deposition of suspended matter occurs predominantly in only a few areas (the Waddensea, the German Bight, the Skagerrak/Norwegian Channel). The remainder of the North Sea floor consists of Pleistocene and Early Holocene relict deposits and of reworked sands and gravels. The mechanisms resulting in accumulation and deposition are discussed. There are strong indications that the amount of suspended matter flowing out from the North Sea into the Norwegian Sea along the Norwegian coast is only little more, or the same, as the amount coming in from the North Atlantic, although its composition may be different.