|Region||Southern Denmark (Syddanmark)|
|Time zone||Central Europe Time (UTC+1)|
||This article may require copy editing for grammar, style, cohesion, tone, or spelling. (January 2013)|
The Arabic geographer Muhammad al-Idrisi mentions in the mid-12th century a landmark Tu(r)ndira, which may be Tønder or possibly the nearby town of Møgeltønder. The Carta Marina of Olaus Magnus shows it as Tunner.
Tønder was granted Hanseatic port privileges in 1243, and is thus Denmark's oldest privileged market town. In 1532 the town was hit by severe flooding, with the water reaching 1.8 metres high in St Laurent's church, 5.3 metres above normal. Tønder's port lost direct access to the sea mainly due to the building of dykes west of the town in the 1550s, at the instigation of Duke Hans the Elder of Schleswig-Holstein-Haderslev (a son of Frederick I of Denmark). The centre of the town is dominated by houses from the late 17th and early 18th century, when the town experienced rapid growth as a result of its lace industry.
Prior to 1864, Tønder was situated in the Duchy of Schleswig, so its history is properly included in the contentious history of Schleswig-Holstein. In the 1920 Schleswig Plebiscite that incorporated Northern Schleswig as part of Denmark, 76.5% of Tønder's inhabitants voted for remaining part of Germany and 23.5% voted for the cession to Denmark.
During World War I, a base for Zeppelin airships was operated at Tønder by the German Navy. The former site now houses a museum, the Zeppelin and Garrison Museum Tønder. The base was attacked by the British on 19 July 1918, during what is known as the Tondern raid. Seven Sopwith Camels from the aircraft carrier HMS Furious bombed the base and two of the three Airship hangars were hit, the Zeppelins L.54 and L.60 inside one hanger were destroyed and a balloon inside the other was damaged. After this, Tondern was abandoned as an active airship base, and ordered to be used only as an emergency landing site. A wartime aircraft hangar survives, as do some of the ancillary buildings from the period, but only the foundations remain of the large airship hangars.
After the First World War Tønder was detached from Germany, even though 77% of the voters had voted to remain with the German Empire in the Schleswig Plebiscites. In the following years German political parties had a majority in the city council. Until 1945, the city was officially bilingual. During World War II, Tønder was the place where the German forces crossed the border to occupy Denmark. Later, Tønder came to host a small, German concentration camp (see Tønder concentration camp). Shortly after the re-establishment of the Danish administration Tønder was the site of a garrison.
After the end of the German occupation in World War II, the political significance of the German part of the population dwindled considerably. The border situation hindered the development of the city. Nevertheless, some companies settled. The importance of tourism increased. Despite the improvement of cross-border traffic, the location was in the late 20th Tønders Century increasingly difficult. In 1989, a teacher training college opened its doors in 2002, the barracks and in the following year the hospital, which is, however, now been enhanced as a private clinic again.
Every August, the Tønder Festival takes place, offering the visitor a wide variety of traditional and modern folk music.The Scouts of Tonder are twinned with Hemyock, in Devon, England, and the scouts make exchange trips every few years.
See also 
Media related to Tønder at Wikimedia Commons