The Wadden lies between the coast of northwestern continental Europe and the range of Frisian Islands, forming a shallow body of water with tidal flats and wetlands.

The Wadden Sea is an intertidal zone in the southeastern part of the North Sea. It lies between the coast of northwestern continental Europe and the range of Frisian Islands, forming a shallow body of water with tidal flats and wetlands. It is rich in biological diversity. In 2009, the Dutch and German parts of the Wadden Sea were inscribed on UNESCO's World Heritage List.

Tthe Wadden Sea is one of the world's seas whose coastline has been most modified by humans, via systems of dikes and causeways on the mainland and low lying coastal islands. The Wadden Sea stretches from Den Helder in the Netherlands in the southwest, past the great river estuaries of Germany to its northern boundary at Skallingen north of Esbjerg in Denmark along a total length of some 500 km and a total area of about 10,000 km². Within the Netherlands it is bounded from the IJsselmeer by the Afsluitdijk.

The islands in the Wadden Sea are called the Wadden Sea Islands or Frisian Islands, named after the Frisians. However, on the westernmost Dutch island, Texel, the Frisian language has not been spoken for centuries. The Danish Wadden Sea Islands have never been inhabited by Frisians. The outlying German island of Heligoland, although ethnically one of the Frisian Islands, is not situated in the Wadden Sea.

The German part of the Wadden Sea was the setting for the 1903 Erskine Childers novel The Riddle of the Sands.