2012 Christmas Card from the Greek Royal Family

The Greek royal family is a branch of the House of Glücksburg that reigned in Greece from 1863 to 1924 and again from 1935 to 1973. Its first monarch was George I, the second son of King Christian IX of Denmark. The line of king George I of the Hellenes is not descended through blood to the last emperors of Byzantium.

After the overthrow in 1862 of the first king of the independent Greek state, Otto of Bavaria, a plebiscite in Greece was initiated on 19 November 1862, with the results announced in February the following year,[note 2] in support of adopting Prince Alfred of the United Kingdom, later Duke of Edinburgh, to reign as king of the country. The candidacy of Prince Alfred was rejected by the Great Powers. The London Conference of 1832 had prohibited any of the Great Powers' ruling families from accepting the crown of Greece, while Queen Victoria was opposed to such a prospect.

A search for other candidates ensued, and eventually, Prince William of Denmark, of the House of Glücksburg, the second son of King Christian IX and younger brother of the new Princess of Wales, was appointed king. The Greek Parliament unanimously approved on 18 March 1863 the ascension to the Greek throne of the prince, then aged 17, as King of the Hellenes under the regnal name of George I. George arrived in Greece in October 1863.

George I married Grand Duchess Olga Constaninovna of Russia, and they had seven surviving children. After a reign of almost fifty years, George I was succeeded by his eldest son, Constantine I, who had married, in 1913, Princess Sophia of Prussia, a granddaughter of Queen Victoria and sister of Kaiser Wilhelm II. In turn, all three of Constantine's sons, George II, Alexander and Paul, would occupy the throne.

The dynasty reigned in Greece during the Balkan Wars, World War I, World War II (during which Greece experienced occupation by the Axis), the Greek Civil War, and the Greek military junta of 1967–1974.

Following the National Schism during World War I and the subsequent Asia Minor Disaster, the monarchy was deposed in March 1924 and replaced by the Second Hellenic Republic. Between 1924 and 1935 there were in Greece twenty-three changes of government, a dictatorship, and thirteen coups d'etat. In October 1935, General Georgios Kondylis, a former Venizelist, overthrew the government and arranged for a plebiscite to end the republic. On 3 November 1935, the official tally showed that 98% of the votes supported the restoration of the monarchy. The balloting was not secret, and participation was compulsory. As Time described it at the time, "As a voter, one could drop into the ballot box a blue vote for George II, or one could cast a red ballot for the Republic." George II returned to the Greek throne on 25 November 1935.

On 4 August 1936, the King endorsed the establishment of a Government led by veteran army officer Ioannis Metaxas.

George II followed the Greek government in exile after the German invasion of Greece in 1941 and returned to the throne in 1946, after a referendum that resulted in the restoration of constitutional monarchy. He died in 1947 and was succeeded by his brother Paul. The new King reigned from the time of Greek civil war until his death in 1964, and was succeeded by his son, Constantine II.

On 21 April 1967, the elected government of Greece was overthrown by a group of middle-ranking army officers led by Colonel Georgios Papadopoulos, and a military dictatorship was established. The military junta formed a new government that was sworn in by Constantine II. On 13 December 1967, the King launched a counter-coup that failed[7] and he, together with his family, fled to Rome and soon after to London.

The dictatorship nominally retained the monarchy but on 1 June 1973, Constantine II was declared "deposed" and Papadopoulos appointed himself "President of the Republic." Some two months later, on 29 July 1973, the military regime held a referendum whose official result confirmed, according to the junta, the abolition of the monarchy.

After July 1974, the dictatorship fell. The military handed power over to Konstantinos Karamanlis, a conservative politician who had been prime minister in the 1950s and early 60s. Karamanlis formed a "government of national unity" and held a constitutional referendum on 8 December 1974. The voters confirmed the abolition of the monarchy by a vote of 69% to 31% and the establishment of a parliamentary democracy in Greece.

In 2013, after being declared personae non gratae in the 1980s, having the palaces of the family and other estates expropriated in 1994, and then their passports annulled, Constantine and his wife Anne-Marie were once again living in Greece.

As male-line descendants of King Christian IX of Denmark, members of the dynasty bear the title of Prince or Princess of Denmark and thus are traditionally referred to as "Princes" or "Princesses of Greece and Denmark".