Dannebrog is the commonly used name in Denmark for Denmark's national flag. It is red with a white cross that reaches the sides of the flag.

Cross flags are known from several places, but predominantly in Northern Europe, primarily the other Nordic countries – Finland, Sweden, Norway and Iceland – as well as the autonomous areas of Åland and the Faroe Islands, and also from the Baltic area, Oldenborg with several places, including as a city flag (e.g. Pärnu in Estonia).

The flag is usually believed to originate from the Danish Crusade period in the 12th-13th centuries. However, the first documented use is in Valdemar Atterdag's coat of arms from the second half of the 14th century. A well-known myth about the origin of the flag states that the flag fell from the sky during Valdemar Sejr's battle at Lyndanisse in 1219 against the Estonians. The earliest versions of the legend, however, place this event in a battle at Fellin in 1208. These are two accounts from the beginning of the 16th century from the theologian and chronicler Christiern Pedersen and the monk Peder Olsen, respectively, which are probably based on the same, now unknown , source.