Looking for a good pub quiz question? This one might catch some people out. Europe has a surprising number of monarchies, ranging from the well known to the obscure. They cover the spectrum from constitutional monarch through power sharing to absolute ruler. The youngest monarchy was instituted in 1929 (and that's a clue).
Currently there are 12 European countries that have a monarch as a head of state. Surprised? Check:
Starting with the obvious, we have HM Queen Elizabeth II in the United Kingdom. She is a constitutional monarch; she is head of state for 16 countries scattered all over the world. She holds additional European domains as Duke of Normandie and Lord of Man that are not considered countries. She is the last of the dynasty of the house of Saxe-Coburg-Gotha which started with Edward VII. Her successor will be a scion of the house of Schleswig-Holstein-Sonderburg-Glücksburg.
The latter brings us to Denmark. HM Queen Margaret II is is the last of the Schleswig-Holstein-Sonderburg-Glücksburg to rule that country. Her successor will be of the house of de Laborde de Monpezat. But not all is lost for the house of Schleswig-Holstein-Sonderburg-Glücksburg (though they lost Greece in 1967); when Norway gained independence from Sweden in 1905, they called in a Danish prince to become their king. Currently Norway is ruled HM King Harald V.
Sweden's Royal line of Holstein-Gottorp (that's the same family as in Denmark and Norway, albeit another branch; it is also the same family that lost Russia in 1918) failed in 1818, parliament elected the French Marshal Bernadotte as heir to the throne (after the chosen Danish prince managed to die of a stroke within a year of being made Crown Prince of Sweden). Currently, HM King Carl XVI Gustav is sitting on that throne.
Coming back to the house of Saxe-Coburg-Gotha, we come to Belgium. When Belgium became independent from the Netherlands in 1830, parliament in Brussels set out to elect a king who had nothing to do with the former Dutch rulers. They elected the French Prince of Orleans, but received in the best French fashion a right royal snub. In a second try they settled on Prince Leopold of Saxe-Coburg-Gotha, the widower of Crown Princess Charlotte of the United Kingdom. HM King Philip rules the Belgians since July 21, 2013.
The Netherlands are ruled by the house of Orange-Nassau under HM King Willem-Alexander since April 30, 2013. In neighboring Luxembourg, the senior house of Nassau-Weilburg is headed by HRH Grand Duke Henri. Luxembourg became independent in 1867 and was ruled by the Kings of the Netherlands until the ascent of Queen Wilhelmina who as a woman could not inherit in Luxembourg. (The same happened to Queen Victoria over the Kingdom of Hanover.)
Spain has been ruled by the house of Bourbon-Anjou since the beginning of the 18th century when they succeeded the Habsburg dynasty. After the interruption caused by the dictatorship of General Franco, the Spanish voters reintroduced the monarchy with a large majority of votes. The current King of Spain is HM King Juan Carlos. This closes the list of Royal Families.
Between Spain and France lies the Principality of Andorra. It has two ruling princes according to treaties between Spain and France, one prince is the Bishop of Urgell, Archbishop Joan Enric Vives i Sicìlia (since 2003), the other is the President of France, François Hollande (since 2012).
Monaco became independent in 1297 and started styling itself a Principality in the 17th century. The ruling house of Grimaldi is represented by HSH Prince Albert II. Until 2002, the Principality would have fallen to France if a ruling prince had died without issue, but that treaty has been redrawn, making HRH Princess Caroline of Monaco Princess of Hanover the current incumbent.
The Principality of Liechtenstein was named after its ruling family, rather than the other way round. The little country sandwiched between Switzerland and Austria is ruled by HSH Prince Hans Adam II. The monarchy is not purely constitutional as the Prince shares the power with his people on an equal footing. As the family predates the country, the constitution of Liechtenstein doesn't cover the succession rights.
And finally, the smallest state in the world is the Vatican. It is ruled by the Pope as an absolute monarch since the Lateran treaties of 1929, currently by HH Pope Francis. He is also, but in a separate role, a religious leader as head of the Catholic Church. He shares that distinction in Europe with HM Queen Elisabeth II as head of the Church of England and HM Queen Margaret II as head of the Danish Episcopal Reformed Church.
A few foot notes might seem in order. The counting in houses is outdated with equal rights for male and female offspring becoming an universal feature in the dynasties ruling in Europe. That, notably, excludes the Liechtenstein family which will be governed by Salian law for as long as they see fit. For those who thought the ruling house in the United Kingdom was called Mountbatten, it is. But the name is one of choice and not of descent. Mountbatten, by the way, is Battenberg in German, a morganatic junior house of Saxe-Coburg-Gotha. And on the latter, just to keep track of the losses, the Saxe-Coburg-Gotha managed to lose Bulgaria.
Last but not least, there is the usual mess about Royal Families and others. The Royals end where I drew the virtual line above; anyone mentioned after that is not of Royal descent. Irritatingly, Princess Caroline of Monaco married into the the Hanoverian Royal line and is addressed as HRH because of that. Her sons Andrea Casiraghi, Pierre Casiraghi, and her daughter Charlotte Casiraghi hold no titles, they are not Prince or Princess of Monaco and rate no Highness.