The Queen will become the longest serving monarch in British history on Wednesday, September 9, overtaking the record previously held by her great-great-grandmother Queen Victoria.
Victoria, who reigned for 63 years and seven months, came to the throne aged 18 and died in 1901 when she was 81.
Elizabeth II, who became Queen aged 25 in 1952, has now entered the history books after reaching the landmark at the age of 89.
Here is a look back at the reigns of the two monarchs.
Accession to the throne and Coronation
Queen Elizabeth's accession to the throne came at the age of 25 in 1952, after her father King George VI died at the age of 56.
Her Coronation took place at Westminster Abbey on 2 June 1953, and was watched by millions.
Queen Victoria acceded to the throne on the 1st June 1837 at the age of 18, after the death of her uncle William IV.
Her father had died shortly after her birth and she became heir to the throne because three uncles who were ahead of her in succession - George IV, Frederick Duke of York, and William IV - had no legitimate children who survived.
Queen Victoria's coronation ceremony took place a year later, on 28 June 1838, at Westminster Abbey.
Victoria married her first cousin Prince Albert of Saxe-Coburg and Gotha in 1840.
They went on to have nine children between 1840 and 1857 who all married into noble families on the continent.
They were Princess Victoria, Prince Albert Edward, Princess Alice, Prince Alfred, Princess Helena, Princess Louise, Prince Arthur, Prince Leopold and Princess Beatrice.
They went on to have 42 children and 37 great-grandchildren earning Victoria the nickname the "grandmother of Europe".
On 20 November 1947, the then Princess Elizabeth married Lieutenant Mountbatten at London's Westminster Abbey.
In 1948, Prince Charles was born, followed by Princess Anne two years later.
Prince Andrew arrived in 1960 and the couple's fourth child, Prince Edward was born in 1964.
The Queen and Duke of Edinburgh have eight grandchildren and five great-grandchildren.
Hobbies and past-times
Queen Victoria is famed both for her stern disposition and devout diary-keeping.
She began keeping a journal at a very young age after being given her first one by her mother.
"This book, Mamma gave me, that I might write the journal of my journey to Wales in it", the 13-year-old Princess Victoria of Kent wrote in 1832.
It became a habit she continued throughout her adult life, including when she became Queen, and her diaries chronicled numerous events including the sudden death of her husband Prince Albert in 1861.
Reflecting on her grief, the queen described how her "sad and suffering heart was soothed and cheered by the excursions and incidents it recounts".
When Victoria died in 1901 at the age of 81, her journals totalled 43,765 pages.
In contrast, Queen Elizabeth is best known for her love of animals.
She has had a lifelong passion for horses and horse racing which is an interest she shared with her mother.
The royals are also famed for having corgis as pets and Queen Elizabeth has owned more than 30 during her reign.
Her first Corgi called Susan was given to her on her 18th birthday but the Queen has said she is now "too old" for any more as she does not want to leave her pets behind when she dies.
In addition to Elizabeth II and Queen Victoria, only four other monarchs in British history have reigned for 50 years or more:
- King George III (59 years)
- King Henry III (56 years)
- Edward III (50 years)
- James VI of Scotland (James I of England) (58 years)