Queen Elizabet II made history last year as she became the first British monarch to celebrate her Platinum Jubilee - 70 years on the throne.
She became the longest-reigning British monarch in September 2015, when she surpassed the reign of her great-great-grandmother, Queen Victoria.
Elizabeth II and Victoria have been the only two British monarchs to reach their Diamond Jubilee.
But six sovereigns have ruled the country for 50 years - reaching their Golden Jubilee.
The nation's longest-reigning monarchs include:
Edward III
Edward III became king when he was 14 in 1327, and reigned for 50 years and 148 days.
He was the monarch who first created the Duchy of Cornwall to provide his eldest son, Edward, the Black Prince, with an income - just as it is still used today for heir to the throne, the Prince of Wales.
He also introduced the Order of the Garter. It remains the highest British order of chivalry, awarded by the sovereign for outstanding public service and achievement.
Edward III's reign saw the beginning of the Hundred Years War against France.
Henry III
Henry III ruled for 56 years and 28 days.
The 13th-century king was only nine when he became monarch in 1216. The country was ruled by a series of regencies until 1234, when Henry took over. His reign was marked with rebellions by barons.
James VI of Scotland
James VI was King of Scotland for 57 years and 246 days.
His mother Mary, Queen of Scots, was forced to abdicate in favour of her infant son in 1567, when James was one. He took full control as a teenager.
He also later became King James I of England and Ireland when Elizabeth I died, and was the assassination target of the Guy Fawkes gunpowder plot.
He was nicknamed The Wisest Fool in Christendom and was the father of Charles I.
George III
George III reigned for 59 years and 96 days - missing out on his Diamond Jubilee by around 10 months.
But, for the last nine years of his life, he was declared mentally unfit to rule, and his son, the Prince of Wales - later George IV - acted as Prince Regent.
George III is widely remembered for two things: losing the American colonies and his so called "madness" - although he is now actually thought to have suffered from a hereditary physical disorder called porphyria.
He died in 1820, when he was 81.
Queen Victoria
Victoria's reign of 63 years and 216 days saw great economic, social and political change.
She was Queen at the age of 18 in 1837 and her time on the throne spanned the rest of the century. She became the figurehead of a vast empire.
Victoria married Prince Albert and had nine children, but mourned her husband's early death for the rest of her life.
She was in ill health by the time she reached her Diamond Jubilee in 1897 and died in 1901, at the age of 81.
Elizabeth II
Queen Elizabeth II became Britain's longest-reigning monarch in 2015.
She overtook the previous record set by her great-great grandmother Victoria at around 5.30pm on September 9, 2015, at the age of 89 - having been head of state for 23,226 days, 16 hours, and some 30 minutes.
She was also one of the world's oldest monarchs and, at one point, was the world's longest-reigning living monarch.
But the world's longest-reigning monarch in history is King Sobhuza II of Swaziland, who died in 1982.
He was just four months old when he became king and ruled for 82 years and 253 days.
It was estimated that he had about 210 children from at least 70 wives and by the time of his death, had more than 1,000 grandchildren.
