Frederick III of Denmark in the context of "Codex Regius"

The monarchy of Denmark is a constitutional institution and an office of the Kingdom of Denmark. The Kingdom includes Denmark proper and the autonomous territories of the Faroe Islands and Greenland. The Kingdom of Denmark was already consolidated in the 8th century, whose rulers are consistently referred to in Frankish sources (and in some late Frisian sources) as "kings" (reges). Under the rule of King Gudfred in 804 the Kingdom may have included all the major provinces of medieval Denmark.

The current unified Kingdom of Denmark was founded or re-united by the Viking kings Gorm the Old and Harald Bluetooth in the 10th century. Originally an elective monarchy, it became hereditary only in the 17th century during the reign of Frederick III. A decisive transition to a constitutional monarchy occurred in 1849 with the writing of the first democratic constitution, replacing the vast majority of the old absolutist constitution. The current Royal House is a branch of the ducal House of Glücksburg, originally from Schleswig-Holstein in modern-day Germany, the House of Glücksburg itself being a collateral branch of the House of Oldenburg. The House of Glücksburg also produced the monarchs of Norway, of the United Kingdom and the former monarch of Greece in the direct male line.

Fredericia (Danish pronunciation: [fʁeðɐˈʁetɕæ, fʁæðɐˈʁætɕæ]) is a town located in Fredericia Municipality in the southeastern part of the Jutland peninsula in Denmark. The city is part of the Triangle Region, which includes the neighbouring cities of Kolding and Vejle. It was founded in 1650 by Frederick III, after whom it was named.

The city itself has a population of 41,543 (1 January 2025) and the Fredericia Municipality has a population of 52,616 (2025).

The Treaty of Roskilde was negotiated at Høje Taastrup Church and was concluded on 26 February (OS) or 8 March 1658 (NS) during the Second Northern War between Frederick III of Denmark–Norway and Karl X Gustav of Sweden in the Danish city of Roskilde. After a devastating defeat, Denmark–Norway was forced to give up a third of its territory to save the rest, the ceded lands comprising Blekinge, Bornholm, Bohuslän, Scania and Trøndelag, as well as Halland.

After the treaty entered into force, Swedish forces continued to campaign in the remainder of Denmark–Norway, but had to withdraw from the Danish isles and Trøndelag in the face of a Dano–Norwegian and Dutch alliance. The Treaty of Copenhagen restored Bornholm to Denmark and Trøndelag to Norway in 1660, while the other provinces transferred in Roskilde remained Swedish.

The Northern War of 1655–1660 was fought between Sweden and the Polish–Lithuanian Commonwealth, with participation at different times by Russia, Brandenburg-Prussia, the Habsburg monarchy, and Denmark–Norway. It ended with the treaties of Copenhagen and Oliva in 1660.

In 1655, Charles X took advantage of the Russo-Polish War (1654–67) to over-run western Poland. The Grand Duchy of Lithuania was annexed by Sweden, and John II Casimir Vasa took refuge in Vienna. He managed to regain parts of his kingdom in 1656, and the conflict widened when Russia declared war on Sweden, supported by Emperor Leopold and Frederick III of Denmark.

This is a list of Danish princes from the establishment of hereditary monarchy by Frederick III in 1648. Individuals holding the title of prince would usually also be styled "His Royal Highness" (HRH) or "His Highness" (HH).