A: The flag of Denmark has been used continuously since January 1st, 1625. The current design of a white Scandinavian cross on a red back ground was adopted in 1625 and its square shape in 1748. In Denmark it is known as the 'Dannebrog' or 'Danish cloth'. Although Denmark was never part of the Roman Empire, similar designs were used by the Empire to represent provinces, as the white cross is symbolic of Christianity.
Other countries that use this Scandinavian or Nordic cross are Sweden, Norway, Iceland, Finland, and the Faroe Islands. Where are the Faroe Islands you ask? They are north of the United Kingdom and west of Norway.
In 2015 the World Happiness Report declared Denmark the 3rd happiest nation in the world! Besides, the cold weather, what's not to love? Universities are free there. The government also pays for 100% of a woman's salary during maternity leave for 52 weeks! Thank you to the people of Denmark for some amazing pastries and this vexillological history lesson.
Sources: Guinness Book of World Records and Gallup, Inc.