As a hereditary constitutional monarchy system, the role and operation of Belgium's monarchy is governed by the Constitution. The royal office of King is designated solely for a descendent of the first King of the Belgians, Leopold I.

Since he is bound by the Constitution[2] (above all other ideological and religious considerations, political opinions and debates and economic interests) the King is intended to act as an arbiter and guardian of Belgian national unity and independence. Belgium's monarchs are inaugurated in a purely civil swearing-in ceremony.

Leopold's son, King Leopold II is chiefly remembered for the founding and exploitation of the Congo Free State which caused global public outrage when human rights abuses were made public. Millions of Congolese were killed as a result of Leopold's policies in the Congo.[6]

Louis Wodon (the chef de cabinet of Leopold III from 1934 to 1940), thought the King's oath to the Constitution implied a royal position "over and above the Constitution". He compared the King to a father, the head of a family, "Regarding the moral mission of the king," said Arango, "it is permissible to point to a certain analogy between his role and that of a father, or more generally, of parents in a family. The family is, of course, a legal institution as is the state. But what would a family be where everything was limited among those who compose it to simply legal relationships? In a family when one considers only legal relationships one comes very close to a breakdown in the moral ties founded on reciprocal affection without which a family would be like any other fragile association"[10] According to Arango, Leopold III of Belgium shared these views about the Belgian monarchy.

In 1991, towards the end of the reign of Baudouin, Senator Yves de Wasseige, a former member of the Belgian Constitutional Court, cited four points of democracy which the Belgian Constitution lacks: 1. the King chooses the ministers, 2. the King is able to influence the ministers when he speaks with them about bills, projects and nominations, 3. the King promulgates bills, and, 4. the King must agree to any change of the Constitution[11]

The Belgian monarchy was from the beginning a constitutional monarchy, patterned after that of the United Kingdom.[12] Raymond Fusilier wrote the Belgian regime of 1830 was also inspired by the French Constitution of the Kingdom of France (1791-1792), the United States Declaration of Independence of 1776 and the old political traditions of both Walloon and Flemish provinces.[13] "It should be observed that all monarchies have suffered periods of change as a result of which the power of the sovereign was reduced, but for the most part those periods occurred before the development of the system of constitutionnal monarchy and were steps leading to its establishment."[14] The characteristic evidence of this is in Great Britain where there was an evolution from the time when kings ruled through the agency of ministers to that time when ministers began to govern through the instrumentality of the Crown.

Unlike the British constitutional system, in Belgium "the monarchy underwent a belated evolution" which came "after the establishment of the constitutional monarchical system"[15] because, in 1830-1831, an independent state, parliamentary system and monarchy were established simultaneously. Hans Daalder, professor of political science at the Rijksuniversiteit Leiden wrote: "Did such simultaneous developments not result in a possible failure to lay down the limits of the royal prerogratives with some precision - which implied that the view of the King as the Keeper of the Nation, with rights and duties of its own, retained legitimacy?" [16]

For Raymond Fusilier, the Belgian monarchy had to be placed - at least in the beginning - between the regimes where the king rules and those in which the king does not rule but only reigns. The Belgian monarchy is closer to the principle "the King does not rule" [17] But the Belgian kings were not only "at the head of the dignified part of the Constitution".[18] The Belgian monarchy is not merely symbolic, because it participates in directing affairs of state insofar as the King's will coincides with that of the ministers, who alone bear responsibility for the policy of government.[19] For Francis Delpérée, to reign does not only mean to preside over ceremonies but also to take a part in the running of the State.[20] The Belgian historian Jean Stengers wrote that "some foreigners believe the monarchy is indispensable to national unity. That is very naive. He is only a piece on the chessboard, but a piece which matters.[21]

The proper title of the Belgian monarch is King of the Belgians rather than King of Belgium. The title King of the Belgians indicates a popular monarchy linked to the people of Belgium (i.e., a hereditary Head of State; yet ratified by popular will). Whereas King of Belgium would indicate standard constitutional or absolute monarchy linked to territory or state.[1] For example, in 1830, King Louis Philippe was proclaimed King of the French rather than King of France. The Greek monarch was titled King of the Hellenes, indicating a personal link with the people, not just the state. Moreover, the Latin translation of King of Belgium would have been Rex Belgii, which from 1815 was the name for the King of the Netherlands. Therefore, the Belgian separatists (i.e. the founders of Belgium) chose Rex Belgarum.[2]

Belgium is the only current European monarchy that does not apply the tradition of the new monarch automatically ascending the throne upon the death or abdication of the previous monarch. According to Article 91 of the Belgian constitution, the monarch accedes to the throne only upon taking a constitutional oath before a joint session of the two Houses of Parliament.[22] The joint session has to be held within ten days of the death of the deceased or abdicated king. The new Belgian monarch is required to take the Belgian constitutional oath, "I swear to observe the Constitution and the laws of the Belgian people, to maintain the national independence and the integrity of the territory," which is uttered in the three official languages: French, Dutch, and German.

Members of the Belgian Royal Family are often known by two names: a Dutch and a French one. For example, the current monarch is called 'Philippe' in French and 'Filip' in Dutch; the fifth King of the Belgians was 'Baudouin' in French and 'Boudewijn' in Dutch.

In contrast to King Philippe's title of "King of the Belgians", Princess Elisabeth is called "Princess of Belgium" as the title "Prince of the Belgians" does not exist. She is also Duchess of Brabant, the traditional title of the heir apparent to the Belgian throne. This title precedes the title "Princess of Belgium".

In the other official language of German, monarchs are usually referred to by their French names. The same is true for English with the exception of Leopold, where the accent is removed for the purpose of simplicity.

Because of the First World War and the resultant strong anti-German sentiment, the family name was changed in 1920 from Saxe-Coburg-Gotha to van België, de Belgique, or von Belgien ("of Belgium"), depending upon which of the country's three official languages (Dutch, French, and German) is in use. It is this family name which is used on the identity cards and in all official documents by Belgium's royalty (e.g. marriage licenses). In addition to this change of name, the armorial bearings of Saxony were removed from the Belgian royal coat of arms (see above). Other Coburgers from the multi-branched Saxe-Coburg family have also changed their name, such as George V of the United Kingdom, who adopted the family name of Windsor after the British Royal Family’s place of residence.[23]

The Belgian monarchy symbolises and maintains a feeling of national unity by representing the country in public functions and international meetings.

In addition, the monarch has a number of responsibilities in the process of the formation of the Government. The procedure usually begins with the nomination of the "Informateur" by the monarch. After the general election the Informateur officially informs the monarch of the main political formations which may be available for governance. After this phase, the monarch can appoint another "informateur" or appoint a "Formateur", who will have the charge of forming a new government, of which he or she generally becomes the Prime Minister.

The Constitution of Belgium entrusts the monarch with federal executive powers: the appointment and dismissal of ministers, the implementation of the laws passed by the Federal Parliament, the submission of bills to the Federal Parliament and the management of international relations. The monarch sanctions and promulgates all laws passed by Parliament. In accordance with Article 106 of the Belgian Constitution, the monarch cannot act without the countersignature of the responsible minister, who in doing so assumes political responsibility. This means that federal executive power is exercised in practice by the Federal Government, which is accountable to the Chamber of Representatives in accordance with Article 101 of the Constitution.

The monarch receives the prime minister at the Palace of Brussels at least once a week, and also regularly calls other members of the government to the palace in order to discuss political matters. During these meetings, the monarch has the right to be informed of proposed governmental policies, the right to advise, and the right to warn on any matter as the monarch sees fit. The monarch also holds meetings with the leaders of all the major political parties and regular members of parliament. All of these meetings are organised by the monarch's personal political cabinet which is part of the Royal Household.

The monarch is the Commander-in-Chief of the Belgian Armed Forces and makes appointments to the higher positions. The names of the nominees are sent to the monarch by the Ministry of Defence. The monarch's military duties are carried out with the help of the Military Household which is headed by a General office. Belgians may write to the monarch when they meet difficulties with administrative powers.

The monarch is also one of the three components of the federal legislative power, in accordance with the Belgian Constitution, together with the two chambers of the Federal Parliament: the Chamber of Representatives and the Senate. All laws passed by the Federal Parliament must be signed and promulgated by the monarch.

Article 88 of the Belgian Constitution provides that "the King's person is inviolable, his ministers are responsible". This means that the King cannot be prosecuted, arrested, or convicted of crimes, cannot be summoned to appear before a civil court, and is not accountable to the Federal Parliament. This inviolability was deemed incompatible, however, with Article 27 of the Rome Statute of the International Criminal Court which states that official capacity shall not exempt a person from criminal responsibility under the statute.[24]

The King's Household (Dutch: Het Huis van de Koning, French: La Maison du Roi, German: Das Haus des Königs) was reorganised in 2006, and consists of seven autonomous departments and the Court's Steering Committee. Each Head of Department is responsible for his department and is accountable to the King.

The following departments currently make up the King's Household:

the Department for Economic, Social and Cultural Affairs

the King's Cabinet

the King's Military Household

the King's Civil List

the Department for Foreign Relations

the Department of the Protocol of the Court

the Department of Petitions

The King's Chief of Cabinet is responsible for dealing with political and administrative matters and for maintaining the relations with the government, trade unions and industrial circles. In relation to the King, the Chief assists in keeping track of current events; informs regarding all aspects of Belgian life; proposes and prepares audiences; assists in preparing speeches and informs the King about developments in international affairs. The Chief of Cabinet is assisted by the Deputy and Legal Adviser, the Press Adviser and the Archivist. The incumbent Chief of Cabinet is Baron Frans Van Daele, former Chief of Cabinet of President of the European Council Herman Van Rompuy.

King Philippe and Queen Mathilde wave to the crowds in Brussels after Philippe's swearing in as new Belgian monarch, 21 July 2013.

The Head of the King's Military Household assists the King in fulfilling his duties in the field of defence. He informs the King about all matters of security, defence policy, the views of Belgium's main partner countries and all aspects of the Belgian Armed Forces. He organises the King's contacts with the Armed Forces, advises in the fields of scientific research and police and coordinates matters with patriotic associations and former service personnel. The Military Household is also responsible for managing the Palace's computer system. The Head of the Military Household is a General Officer, currently GeneralJef Van den put and assisted by an adviser, currently Lieutenant-ColonelAviatorSerge Vassart. The King's Aides-de-Camp and the King's Equerries are also attached to the Military Household.

The King's aides-de-camp are senior officers chosen by the monarch and charged with carrying out certain tasks on his behalf, such as representing him at events. The King's Equerries are young officers who take turns preparing the King's activities, informing him about all the aspects that may be important to him and providing any other useful services such as announcing visitors. The equerry accompanies the King on his trips except for those of a strictly private nature.

The Intendant of the King's Civil List is responsible for managing the material, financial and human resources of the King's Household. He is assisted by the Commandant of the Royal Palaces, the Treasurer of the King's Civil List and the Civil List Adviser. The Intendant of the Civil List also advises the King in the field of energy, sciences and culture and administers the King's hunting rights. The Commandant of the Royal Palaces is mainly in charge, in close cooperation with the Chief of Protocol, of the logistic support of activities and the maintenance and cleaning of the Palaces, Castles and Residences. He is also Director of the Royal Hunts.

The Chief of Protocol is charged with organising the public engagements of the King and the Queen, such as audiences, receptions and official banquets at the Palace, as well as formal activities outside of the Palace. He is assisted by the Queen's Secretary, who is mainly responsible for proposing and preparing the Queen's audiences and visits.

The Royal palace is used for state occasions at court.

The Head of the Department for Economic, Social and Cultural Affairs advises the King in the economic, social and cultural fields. He is also responsible for providing coordination between the various Households and Services and for organising and minuting the meetings of the Steering Committee. The Head of the Department for Foreign Relations informs the King of developments in international policy, assists the King from a diplomatic viewpoint on royal visits abroad and prepares the King's audiences in the international field. He is also responsible for maintaining contacts with foreign diplomatic missions. The Head of the Department of Petitions is charged with processing petitions and requests for social aid addressed the King, the Queen or other members of the Royal Family. He is also responsible for the analysis and coordination of royal favours and activities relating to jubilees, and advises the King in the fields for which he is responsible.

For the personal protection of the King and the Royal Family, as well as for the surveillance of the royal estates, the Belgian Federal Police at all times provides a security detail to the Royal Palace, commanded by a chief police commissioner.

There are currently two other Households at the Belgian Court: the Household of Her Majesty Queen Fabiola and the Household of Their Royal Highnesses the Duke and Duchess of Brabant. The other members of the Royal Family have a service at their disposal.

Members of the Royal Family hold the title Prince (Princess) of Belgium with the style of Royal Highness. Prior to World War I they used the additional titles Prince (Princess) of Saxe-Coburg and Gotha and Duke (Duchess) of Saxony as members of the House of Wettin.

Philippe is HM The King of the Belgians, born 15 April 1960. He married, on 4 December 1999, JonkvrouweMathilde d'Udekem d'Acoz, who was created HRH Princess Mathilde of Belgium, Duchess of Brabant a day before their wedding, and became, from 21 July 2013, HM Queen Mathilde of the Belgians. She is a daughter of the late Patrick d'Udekem d'Acoz (made a count prior to the wedding) and his wife, Countess Anna Maria Komorowska. They have four children:

HM King Albert II (born 6 June 1934). He was the king between 1993 (following the death of his brother King Baudouin) and 21 July 2013, the Belgian National Day, when he abdicated in favour of his son Philippe, Duke of Brabant, because of ill health. On 2 July 1959 he married Donna Paola Ruffo di Calabria (born 11 September 1937) in Brussels, who was created HRH Princess Paola of Belgium, Princess of Liège a day before their wedding, and after 1993, became Queen Paola of the Belgians. She is the daughter of Fulco VIII, Prince Ruffo di Calabria, 6th Duke of Guardia Lombarda (1884-1946) and his wife, Luisa Gazelli dei Conti di Rossana e di Sebastiano (1896–1989). Together they have three children, the current king (see above), a daughter and another son:

HI&RH Princess Astrid, Archduchess of Austria-Este (born 5 June 1962). She is the wife of HI&RH Prince Lorenz of Belgium, Archduke of Austria-Este, Prince Royal of Hungary and Bohemia, whom she married on 22 September 1984 and who was created a prince of Belgium in 1995. Princess Astrid, with her own descendants, is before her brother Laurent in the order of succession to the Belgian throne, due to the 1991 act of succession mentioned above. They have five children:

HRH Prince Laurent of Belgium (born 19 October 1963). He married Claire Coombs, an Anglo-Belgian former land surveyor, on 12 April 2003, who was created HRH Princess Claire of Belgium 11 days before their wedding. They have one daughter and two sons:

HRH Princess Marie-Esméralda, Lady Moncada (born 30 September 1956). She is the youngest daughter of Leopold III and Lilian, Princess of Réthy, half-sister of both Kings Baudouin and Albert II and half-aunt of The King Philippe. Princess Marie-Esméralda is a journalist, writing under the name Esméralda de Réthy'. She married Sir Salvador Moncada, a Honduran-British pharmacologist, in London on 4 April 1998. They have a daughter, Alexandra Leopoldine (born in London on 4 August 1998), and a son, Leopoldo Daniel (born in London on 21 May 2001).