The present head of the British monarchy, Queen Elizabeth II, has been on the throne since 1952 and is the only head of state in the world to reign over more than one independent country - she is officially Queen of no less than sixteen other states, including Australia and Canada. The monarch of the UK is not only the official head of state of this country and its dependent territories, but also head of the Commonwealth.
The present Royal family can trace its lineage all the way back to the 9th century Kings of Wessex. In the past the British monarchy held absolute power over its subjects, but nowadays their role is perceived as more ceremonial - the State Opening of Parliament for instance - with government acting by consent rather than by order.
As an institution, the monarchy is Britain's largest landowner and many of the royal residences are major tourist attractions.
The British Monarchy as we now know it is a far cry from its beginnings: after the Viking invasions of the 9th century, the first recognisable English kings - starting with Alfred the Great - begun to hold sway. But it was only when England was overrun by the Normans, and the reign of William the Conqueror commenced, that a centralised system of Royal rule was established.
For much of the UK's history it hasn't been such a united kingdom with England and Scotland being reigned over by separate monarchies but, following the death of the childless Elizabeth the First, King James of Scotland became the successor to the English throne and the union was forged; the 1707 Acts of Union cemented this bond.
Since its inception, there has only been one break in the line of English monarchs, when Oliver Cromwell emerged victorious from the English Civil War, overthrew and executed the king and pronounced himself to be Lord Protector. After Cromwell's death, the monarchy reformed and went to the lengths of exhuming Cromwell's buried body and and beheading it! The head subsequently had a succession of owners but in 1960 was finally laid to rest in the grounds of Sidney Sussex College (University of Cambridge).