Originally an elective monarchy including also Scania (the southern part of present Sweden), and various Scandinavian territories; one of the earliest Kings, Knud I (Canute) (d 1035) also ruled much of England. The throne did not become hereditary until the 12th century and neither legitimacy nor primogeniture was necessarily required. King Knud IV (1163-1202) assumed title of King of the Slavs following the subjection of the Slavic tribes in Northern Germany 1184, this title changed to King of the Wends by King Waldemar IV (d 1375), who also assumed the title of King of the Goths after the conquest of Gotland 1361. The male line of the ancient Kings expired with the death of Waldemar IV in 1375. His daughter, Margaret (1353-1412) m Haakon VI, King of Norway and Sweden (d 1380); their son Oluf III (d 1387) united all three Crowns. Waldemar's elder daughter, Ingeborg, m Duke Henry of Mecklenburg and had issue Mary (1363-1402?) who m Wartislav VII, Duke of Pomerania; their son Eric VII (d 1459) became King of Norway 1389, of Denmark and Sweden 1396, and was crowned King of the Union 1397 (dethroned 1439). Eric's sister Catherine m 1407 John of Bavaria, Count Palatine of Neumarkt, and had issue a son Christopher III (d 1448), King of Denmark 1440, Sweden 1441, and Norway 1442. He m 1445 Dorothea of Brandenburg (d 1490) who m 2ndly 1449 Christian VIII, Count of Oldenburg and Delmenhorst (d 1481), maternally a 6th generation descendant of King Eric V (1249-1286) (see OLDENBURG for the early origins of this family). Christian of Oldenburg elected Christian I, King of Denmark 1448 and Norway 1450, reigned as King of Sweden 1457-64, Duke of Schleswig and Count of Holstein, Stormarn and Dithmarschen, etc 1460 (Duke from 1474). He was ancestor of the Kings of Denmark, who also reigned as Kings of Norway (until 1814), Sweden (1497-1501 and 1520-23), Dukes of Schleswig, Holstein, Stormarn and Ditmarschen (until 1866), and of Lauenburg (1816-64), and as Counts of Oldenburg and Delmenhorst (1667-1773), and the junior lines which reigned as Counts, Dukes and Grand Dukes of Oldenburg (1773-1918), Emperors of Russia (1762-1917) and Kings of Sweden (1751-1818), as well as a King of Livonia (1570-77), etc. The senior male line of the Kings of Denmark became extinct with the death of King Frederik VII (b 6 Oct 1808; d 15 Nov 1863), Head of the House of Oldenburg. Christian, Prince of Schleswig-Holstein-Sonderburg-Glücksburg, later Christian IX, King of Denmark, son of Duke Wilhelm of Schleswig-Holstein-Sonderburg-Glücksburg (b 4 Jan 1785; d 17 Feb 1831), was designated as immediate successor to his kinsman, King Frederik VII by Treaty dated 8 May 1852 and the revised Danish Law of Succession of 31 July 1853. The Danish province of Iceland became an independent Kingdom 1 Dec 1918 but remained in personal union with Denmark; autonomous Iceland Regency declared 17 May 1941, proclamation of the Republic of Iceland 19 Jun 1944. A new law allowing for the succession of females to the throne, limiting succession to the descendants of King Christian X, was passed by Parliament 27 March 1953 and by referendum 5 June 1953. With the accession of Queen Margrethe II 1972 the use of the titles of King of the Wends and Goths, Duke of Schleswig, Holstein, Stormarn, Dithmarschen, Lauenburg and Oldenburg were abandoned (even though all descendants in the male line enjoy the Schlesvig, Holstein titles by right).

Members of the Royal Family bear the title of Prince or Princess of Denmark with the qualification of Royal Highness for the children of the Monarch and that of Highness for cadet members, following the Cabinet Order of 23 Sept 1774, unless otherwise decided. The throne passes by mixed succession, males having priority over females in each generation.