Hedeby (Danish pronunciation: [ˈheːð̩byːˀ], Old Norse Heiðabýr, German Haithabu) was an important Viking Age (8th to the 11th centuries) trading settlement near the southern end of the Jutland Peninsula, now in the Schleswig-Flensburg district of Schleswig-Holstein, Germany. It is the most important archaeological site in Schleswig-Holstein.
The settlement developed as a trading centre at the head of a narrow, navigable inlet known as the Schlei, which connects to the Baltic Sea. The location was favorable because there is a short portage of less than 15 km to the Treene River, which flows into the Eider with its North Sea estuary, making it a convenient place where goods and ships could be ported overland for an almost uninterrupted seaway between the Baltic and the North Sea and avoid a dangerous and time-consuming circumnavigation of Jutland, providing Hedeby with a role similar to later Lübeck. Hedeby was the second largest Nordic town during the Viking Age, after Uppåkra in present-day southern Sweden, The city of Schleswig was later founded on the other side of the Schlei. Hedeby was abandoned after its destruction in 1066.
Hedeby was rediscovered in the late 19th century and excavations began in 1900. The Haithabu Museum was opened next to the site in 1985.
The Old Norse name Heiða-býr simply translates to "heath-settlement" (heiðr "heath" and býr = "yard; settlement, village, town"). The name is recorded in numerous spelling variants.