Tönning (German; Low German Tünn, Tönn or Tönnen; Danish: Tønning; North Frisian: Taning) is a town in the district of Nordfriesland in the German state of Schleswig-Holstein.

Tönning was destroyed in the Burchardi flood in 1634. During the Great Northern War, (1700–1721), Tönning was besieged twice.

It is located on the northern bank of the Eider river, approximately eight kilometers away from its mouth at the North Sea. Tönning has a population of some 5,000 people.

Tönning is connected by a regional train with Sankt Peter-Ording to the West, and Husum to the North-East. Tönning is also served by several bus routes.

• Eiderstedt peninsula
• Eider Barrage

• Friedrich Wilhelm Selck (1821–1911), councilor of commerce, honorary citizen since 1899
• Friedrich von Esmarch (1823–1908), German physician and the founder of the civilian Samaritan system in Germany, honorary citizen since 1897; there is a memorial statue dedicated to him in the castle park.

• Jürgen Ovens (1623–1678), painter, portraitist
• Johann Friedrich Alberti (1642–1710), composer, organist
• Fanny Suenssen (1832–1918), Danish novelist and short story writer
• Teckla Juel (1834–1904), Danish writer and composer.
• Kurt Thomas (1904–1973), composer, music educator and chorus leader

• Hinrich Braren (1751–1826), captain, pilot and navigation instructor, died in Tönning. He wrote the first German-language textbook of shipping.