The Queen will mark 70 years on the throne this June with the climax of her Platinum Jubilee celebrations.
Four royal events are planned from 3-6 June with highlights including Trooping the Colour, the Party at the Palace and a Big Jubilee Lunch that will see hundreds of street parties up and down the country.
The festivities will give Britons – along with millions around the world – the chance to reflect on the life of one of the most significant individuals of the past 100 years.
The UK's longest-reigning monarch may have taken on fewer duties in recent months amid poor health, but her life has been marked by some of the biggest moments in recent UK history.
Here are nine of the most significant moments of the Queen's reign:
1. Her coronation
Queen Elizabeth II was crowned on 2 June 1953 at the age of 25.
She succeeded the throne from her father George VI, who reigned throughout the Second World War but died at the relatively young age of 56.
She had technically already been head of state since 6 February 1952, which is the day her father died.
At the time of her coronation, she was proclaimed Queen of the UK, Canada, Australia, New Zealand, South Africa, Pakistan and Ceylon (now Sri Lanka).
Read more: Why does the Queen have two birthdays?
More than 8,000 guests attended the ceremony at Westminster Abbey, which lasted almost three hours.
The coronation drew global attention and it was the first one to ever be fully televised.
Millions of people across the UK bought their first television just to watch the event and as many as 17 people on average crammed around each tiny black and white TV.
Although complete figures are hard to come by it has been estimated as many as 277 million people watched the event, which was around 10% of the world's population at the time.
Although no definitive date can be placed on the decolonisation of the British Empire, it was one of the most defining themes of the 20th century and saw the Queen's role across the world changed.
In the 60s and 70s, more than 20 countries gained independence from Britain.
Pakistan dropped the Queen and became a republic in 1956, just four years into her reign, while Sri Lanka replaced her in 1972.
Many other nations in Africa, the Middle East and Southeast Asia also became independent nations, formally ending their role as a protectorate within the British Empire.
The Queen's role has transformed during her reign from being head of state for hundreds of millions of people to instead leading the Commonwealth of Nations, whose membership includes most of the UK's former colonies.
3. Annus horribilis
For the first few decades of her reign, the Queen was immensely popular and besides a few royal and political scandals managed to avoid major difficulty.
But in 1992 a series of events led the monarch to describe the year as her "annus horribilis" – Latin for "horrible year".
The year coincided with her Ruby Jubilee, marking 40 years on the throne.
In a speech marking the occasion, she said: "1992 is not a year on which I shall look back with undiluted pleasure. In the words of one of my more sympathetic correspondents, it has turned out to be an 'annus horribilis."
The scandals included:
The Duke of York's divorce from the Duchess of York.
The divorce of Anne, Princess Royal, from Captain Mark Phillips.
The publication of Diana, Princess of Wales's book Diana: Her True Story revealing the problems between her and Prince Charles, as well as his affair.
Publication of photos of the Duchess of York sunbathing topless
In November there was also a major fire in Windsor Castle, the Queen's official residence. The cost of repairs led to the castle being opened to the public and to the Queen agreeing to pay income tax.
4. Death of Diana
The Prince of Wales's first wife Diana had endured a turbulent relationship with the Royal Family for years.
Her activism and glamour made her an international icon but also subjected her to an extreme amount of public scrutiny.
The public difficulties with her marriage were constantly in the press, but despite this many people remained supportive of the Royal Family.
Public perception changed when she died in a car crash in Paris in August 1997, a year after her divorce from Charles.
Her death caused an unprecedented outpouring of grief from around the world and particularly in the UK.
Some 2.5 billion people watched the funeral on TV.
The Queen expressed her "deep shock" at the news but she faced fierce criticism from the British press over her initial response to the death, which saw her reman at Balmoral Castle with Charles, William and Harry, where they had been holidaying at the time.
Her lack of presence in London led to outrage, although later accounts claimed she remained in Balmoral to be with her grieving grandchildren.
5. Golden Jubilee
Ten years later, her reputation had recovered and the Queen celebrated her 50th anniversary on the throne at her Golden Jubilee.
2002 also marked a difficult time for the Queen as well due to her sister Princess Margaret's and her mother Elizabeth's death early on in the year.
Despite the deaths, the whole of the Commonwealth celebrated the jubilee.
The Queen attended all of the official celebrations completing a more than 40,000 mile global trip with her husband, the Duke of Edinburgh.
6. Ireland Visit
In May of 2011, the Queen made a historic state visit to the Republic of Ireland.
It was the first time a British monarch had visited the areas of the Republic of Ireland in 100 years, when George V made his coronation year visit in 1911, when the entire island was still part of the UK.
The Royal Family has had a complicated relationship with Ireland and is viewed by many as a symbol of British imperialism.
The visit was seen as hugely symbolic for healing historic wounds, especially in the aftermath of the end of the Northern Irish Troubles and the Good Friday Agreement of 1998.
She gave a widely praised speech at Dublin Castle during the trip where she spoke briefly in the Irish language, which was once banned under British rule.
The speech focused on the history between the UK and Ireland and was universally applauded by the Irish media and even some senior anti-royal figures in the both the Republic and Northern Ireland.
7. Diamond Jubilee and the London Olympics
In 2012 the Queen marked 60 years on the throne, and as with previous jubilees, celebrations were thrown across her realms.
This was only the second Diamond Jubilee to be celebrated by a British monarch, after Queen Victoria's in 1897.
Celebrations culminated in the Diamond Jubilee Pageant in June which saw the Thames host a parade of 1,000 boats from around the Commonwealth - the largest flotilla seen on the river in 350 years.
This time the Queen stayed in the UK, while her children toured the world.
While on a visit to Manchester the Queen made a surprise appearance at a wedding at the city's Town Hall, making international headlines.
She also opened the 2012 Summer Olympic Games in London, and appeared in a short film alongside Daniel Craig's James Bond.
8. Longest-reigning monarch
The Queen is currently the world's longest-reigning monarch, the world's oldest and longest-serving head of state, the longest ever female serving head of state and the longest ever reigning monarch to sit on the British throne.
She overtook Queen Victoria on 9 September 2015 and is now in her 70th year on the throne, meaning she is also the first-ever British monarch to celebrate a platinum jubilee.
If she is still reigning on 27 May 2024 she will become the longest ever reigning monarch, taking over from Louis the XIV of France, who reigned for 72 years and 110 days.
9. Death of Prince Philip
On 9 April, the Queen's husband and rock, Prince Philip, died aged 99 after 74 years of marriage.
Prince Philip had retired from public duties in 2017 and spent most of his time at Windsor.
When the COVID-19 pandemic started, he and the Queen retired to Windsor and he was rarely seen.
The Duke of Edinburgh had been the Queen's steadfast companion for most of her life and millions from around the world attended tribute services.
The Queen was pictured sitting on her own during the limited funeral on 17 April 2021 due to the COVID restrictions, an image that is likely to become an enduring symbol of the pandemic.
A full service marking his life was held on 29 March 2022.