The Flag of Denmark (Danish: Dannebrog) is red with a white Scandinavian cross that extends to the edges of the flag; the vertical part of the cross is shifted to the hoist side.

A banner with a white-on-red cross is attested as having been used by the kings of Denmark since the 14th century. An origin legend with considerable impact on Danish national historiography connects the introduction of the flag to the Battle of Lyndanisse of 1219.

A tradition recorded in the 16th century traces the origin of the flag to the campaigns of Valdemar II of Denmark (r. 1202–1241). The oldest of them is in Christiern Pedersen's "Danske Krønike", which is a sequel to Saxo’s Gesta Danorum, written 1520–23. Here, the flag falls from the sky during a Russian campaign of Valdemar's. Pedersen also states that the very same flag was taken into exile by Eric of Pomerania in 1440.

The second source is the writing of the Franciscan monk Petrus Olai (Peder Olsen) of Roskilde (died c. 1570). This record describes a battle in 1208 near a place called "Felin" during the Estonia campaign of King Valdemar II. The Danes were all but defeated when a lamb-skin banner depicting a white cross falls from the sky and miraculously leads to a Danish victory.