The House of Glücksburg (also spelled Glücksborg), shortened from House of Schleswig-Holstein-Sonderburg-Glücksburg, is a Dano-German branch of the House of Oldenburg, members of which have reigned at various times in Denmark, Norway, Greece and several northern German states.

Queen Margrethe II of Denmark, King Harald V of Norway, King Constantine II of Greece, Queen Sofía of Spain and Prince Philip, Duke of Edinburgh (and his eldest son and heir to the British throne Charles, Prince of Wales) are patrilineal members of cadet branches of the Glücksburg dynasty.^[2][3][4]

The family takes its ducal name from Glücksburg, a small coastal town in Schleswig, on the southern, German side of the fjord of Flensburg that divides Germany from Denmark.^[3] In 1460, Glücksburg came, as part of the conjoined Dano-German duchies of Schleswig and Holstein, to Count Christian VII of Oldenburg whom, in 1448, the Danes had elected their king as Christian I, the Norwegians likewise taking him as their hereditary king in 1450.^[3]

In 1564, Christian I's great-grandson, King Frederick II, in re-distributing Schleswig and Holstein's fiefs, retained some lands for his own senior royal line while allocating Glücksburg to his brother Duke John the Younger (1545-1622), along with Sonderburg, in appanage.^[3] John's heirs further sub-divided their share and created, among other branches, a line of Schleswig-Holstein-Sonderburg dukes at Beck (an estate near Minden bought by the family in 1605), who remained vassals of Denmark's kings.^[3]

By 1825, the castle of Glücksburg had returned to the Danish crown (from another ducal branch called Glücksburg, extinct in 1779) and was given that year by King Frederick VI, along with a new ducal title, to his kinsman Frederick of Schleswig-Holstein-Sonderburg-Beck.^[5] Frederick suffixed the territorial designation to the ducal title he already held, in lieu of "Beck" (an estate the family had, in fact, sold in 1745).^[3] Thus emerged the extant Dukes of Schleswig-Holstein-Sonderburg-Glücksburg.

The Danish line of Oldenburg kings died out in 1863, and the elder line of the Schleswig-Holstein family became extinct with the death of the last Augustenburg duke in 1931. Thereafter, the House of Glücksburg became the senior surviving line of the House of Oldenburg. Another cadet line of Oldenburgs, the Dukes of Holstein-Gottorp, consisted of two branches which held onto sovereignty into the 20th century. But members of the Romanov line were executed in or exiled from their Russian Empire in 1917, while the Grand Duchy of Oldenburg was abolished in 1918, although its dynastic line survives.^[3]

Neither the Dukes of Beck nor of Glücksburg had been sovereign rulers; they held their lands in fief from the ruling Dukes of Schleswig and Holstein, i.e. the Kings of Denmark and (until 1773) the Dukes of Holstein-Gottorp.

Prince Christian of Schleswig-Holstein-Sonderburg-Glücksburg, the fourth son of Duke Friedrich of Glücksburg, was recognized in the London Protocol of 1852 as successor to the childless King Frederick VII of Denmark. He became King of Denmark as Christian IX on 15 November 1863.^[3]

Prince Vilhelm, the second son of Crown Prince Christian and Crown Princess Luise, was elected King of the Hellenes on 30 March 1863, succeeding the ousted Wittelsbach Otto of Greece and reigning under the name George I.

Prince Carl, the second son of Frederick VIII of Denmark, Christian IX's eldest son, became King of Norway on 18 November 1905 as Haakon VII of Norway.

Christian IX's daughters, Alexandra of Denmark and Dagmar of Denmark (as Maria Feodorovna) became the consorts of, respectively, Edward VII of the United Kingdom and Alexander III of Russia. As a result, by 1914 descendants of King Christian IX held the crowns of several European realms, and he became known as the "Father-in-law of Europe".

Christian IX's older brother inherited formal headship of the family as Karl, Duke of Schleswig-Holstein-Sonderburg-Glücksburg. It is his descendants who now represent the senior line of the Schleswig-Holstein branch of the House of Oldenburg.

The Dukes of Schleswig-Holstein-Sonderburg-Glücksburg constitute the senior male line of the branch. They hold the headship by primogeniture of the cadet house of Glücksburg. The headship by agnatic primogeniture of the entire House of Oldenburg is held by Christoph, Prince of Schleswig-Holstein.

The heir apparent is Friedrich Ferdinand, Hereditary Prince of Schleswig-Holstein (b. 1985).

In 1853, Prince Christian of Schleswig-Holstein-Sonderburg-Glücksburg became heir to the Kingdom of Denmark, and in 1863, he ascended the throne. He was the third son of Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg, whose elder brother (and male-line descendants) retained the Glücksburg dukedom. The Danish royal family call itself Glücksborg, using a slightly Danicized form of Glücksburg.

The heir apparent is Frederik, Crown Prince of Denmark (b. 1968), who belongs agnatically to the Monpezat family. See the present line of succession. Although there are no more male members of the dynastic line of Glũcksburgs domiciled in Denmark, there are descendants of Christian IX who married without the monarch's permission, thus forfeiting their royal status.^[6] They bear the Danish noble title "Count of Rosenborg" (and the style of Excellency), heritable by their descendants in the legitimate male line.

In 1863 and with the name George I, Prince Wilhelm of Denmark was elected King of the Hellenes on the recommendation of Europe's Great Powers. He was a younger son of King Christian IX of Denmark.

The Hellenic constitutional monarchy was usurped in a coup d'état by a military junta in 1968 and the royal family fled into exile. In a 1974 referendum, 69.18% of the voters decided against the return of the monarchy.

In 1905 and with the name Haakon VII, Prince Carl of Denmark became King of Norway. His father was King Frederick VIII of Denmark, and one of his uncles was King George I of Greece.

The heir apparent is Crown Prince Haakon of Norway (b. 1973). See the present line of succession.

In 1918, Iceland was elevated from an autonomous Danish province to a separate Kingdom of Iceland. Christian X of Denmark was henceforth King of Denmark and Iceland until 1944, when Iceland dissolved the union between the two countries.

The heir apparent was his son Frederick IX of Denmark (1899–1972).

In 1947, Prince Philip of Greece and Denmark (who relinquished his princely titles and adopted the surname of Mountbatten upon becoming a British subject prior to his wedding) was created Duke of Edinburgh by his father-in-law, George VI. Descendants in the male line of his marriage to Queen Elizabeth II belong, by decree, to the House of Windsor and use "Mountbatten-Windsor" as a surname, when one is needed. The first twenty places in the line of succession to the British throne are held by the Duke's descendants.

The heir-apparent is Charles, Prince of Wales (born 1948).^[1]