The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Sea in the north. It is more than 970 kilometres (600 mi) long and 580 kilometres (360 mi) wide, covering 570,000 square kilometres (220,000 sq mi).

It hosts key north European shipping lanes and is a major fishery. The coast is a popular destination for recreation and tourism in bordering countries, and a rich source of energy resources, including wind and wave power.

The North Sea has featured prominently in geopolitical and military affairs, particularly in Northern Europe, from the Middle Ages to the modern era. It was also important globally through the power northern Europeans projected worldwide during much of the Middle Ages and into the modern era. The North Sea was the centre of the Vikings' rise. The Hanseatic League, the Dutch Republic, and Britain all sought to gain command of the North Sea and access to the world's markets and resources. As Germany's only outlet to the ocean, the North Sea was strategically important through both world wars.

The coast has diverse geology and geography. In the north, deep fjords and sheer cliffs mark much of its Norwegian and Scottish coastlines respectively, whereas in the south, the coast consists mainly of sandy beaches, estuaries of long rivers and wide mudflats. Due to the dense population, heavy industrialisation, and intense use of the sea and the area surrounding it, various environmental issues affect the sea's ecosystems. Adverse environmental issues – commonly including overfishing, industrial and agricultural runoff, dredging, and dumping, among others – have led to several efforts to prevent degradation and to safeguard long-term economic benefits.

The North Sea is bounded by the Orkney Islands and east coast of Great Britain to the west and the northern and central European mainland to the east and south, including Norway, Denmark, Germany, the Netherlands, Belgium, and France. In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively. In the north it is bordered by the Shetland Islands, and connects with the Norwegian Sea, which is a marginal sea in the Arctic Ocean.

The North Sea is more than 970 kilometres (600 mi) long and 580 kilometres (360 mi) wide, with an area of 750,000 square kilometres (290,000 sq mi) and a volume of 54,000 cubic kilometres (13,000 cu mi). Around the edges of the North Sea are sizeable islands and archipelagos, including Shetland, Orkney, and the Frisian Islands. The North Sea receives freshwater from a number of European continental watersheds, as well as the British Isles. A large part of the European drainage basin empties into the North Sea, including water from the Baltic Sea. The largest and most important rivers flowing into the North Sea are the Elbe and the Rhine – Meuse. Around 185 million people live in the catchment area of the rivers discharging into the North Sea encompassing some highly industrialized areas.

For the most part, the sea lies on the European continental shelf with a mean depth of 90 metres (300 ft). The only exception is the Norwegian trench, which extends parallel to the Norwegian shoreline from Oslo to an area north of Bergen. It is between 20 and 30 kilometres (12 and 19 mi) wide and has a maximum depth of 725 metres (2,379 ft).

The Dogger Bank, a vast moraine, or accumulation of unconsolidated glacial debris, rises to a mere 15 to 30 m (50 to 100 ft) below the surface. This feature has produced the finest fishing location of the North Sea. The Long Forties and the Broad Fourteens are large areas with roughly uniform depth in fathoms (forty fathoms and fourteen fathoms or 73 and 26 m or 240 and 85 ft deep, respectively). These great banks and others make the North Sea particularly hazardous to navigate, which has been alleviated by the implementation of satellite navigation systems. The Devil's Hole lies 320 kilometres (200 mi) east of Dundee, Scotland. The feature is a series of asymmetrical trenches between 20 and 30 kilometres (12 and 19 mi) long, one and two kilometres (0.6 and 1.2 mi) wide and up to 230 metres (750 ft) deep.