Which peninsula contains the Danish mainland and extends into northern Germany?

The Jutland Peninsula contains the Danish mainland and extends into northern Germany.

Jutland projects northward between the North Sea and the Baltic Sea system. Most of the peninsula belongs to Denmark, while its southern portion forms the German state of Schleswig-Holstein. The Danish–German border crosses the peninsula near its southern end.

Denmark’s mainland is often called Jutland, although the geographic peninsula also includes German territory. The Limfjord cuts across northern Jutland, and the area north of it is sometimes treated as the North Jutlandic Island because the waterway connects the North Sea with the Kattegat.

Jutland has long been a bridge between Scandinavia and continental Europe. Its position supported seaborne trade and helped make the Danish straits strategically important. The peninsula should not be confused with the entire Kingdom of Denmark, which also includes Zealand, Funen, Bornholm, Greenland, and the Faroe Islands.