After more than six decades as head of state, the Queen remains an important figure in national life – a reassuring presence in an ever-changing world.
Revered by her family, a figurehead for the country and one of the most famous faces on the planet, she continues to be an influential individual at home and abroad.
Now in her 91st year, the monarch's longevity means she has seen huge social, political and technological changes during her reign, which today reaches the milestone of 65 years.
When she acceded to the throne on February 6, 1952, Britain was in the grip of post-war austerity, with some goods still rationed and bomb sites blighting the capital and other major cities.
Today the landscape is very different, with Britain rebuilt in the intervening decades, the country a leading G7 nation and soon to begin the process of leaving the European Union.
With the passing years have come milestones: first, becoming Britain's longest-reigning monarch – passing her great-great grandmother Queen Victoria's record in September, 2015.
Then, with the death of 88-year-old King Bhumibol Adulyadej of Thailand last autumn, the Queen is at the age of 90 now the world's longest-reigning living monarch.
The Queen and Duke of Edinburgh's 70th wedding anniversary will be celebrated this year – on November 20 – a union that appears as successful as it has been long.
Decisions have been taken in recent years which have been interpreted as acknowledgement of the monarch's advancing years.
The Queen continues to carry out a full programme of engagements but her long-haul flights have been under review for some period.
For a number of years, some investitures have been staged at Windsor Castle to allow the Queen more time at her favoured Berkshire home.
Before Christmas the head of state stepped down as patron of 25 organisations – some she had been associated with for decades – with members of the Royal Family taking on the patronages.
And the Duke of Cambridge has announced he will be leaving his job as an air ambulance helicopter pilot to spend more time in London with his family, as he and wife Kate want to increase their official duties on behalf of the Queen and their own charity work.
Little is known about the real woman behind the crown, and to some she is seen as remote and less approachable than other European royals, while others believe she is a great British institution and deserves respect.
Away from the trappings of state, her love of horses, racing and her corgis, the short-legged dogs which mill around Buckingham Palace, have been her lifelong interests. Princess Elizabeth Alexandra Mary was born at 2.40am on April 21, 1926, at 17 Bruton Street in Mayfair.
But the abdication of her uncle, Edward VIII, in 1936 changed everything, leaving her father King and making the then Princess Elizabeth the heir presumptive.
Looking forward to her destiny, she pledged in a radio broadcast made in 1947 to serve the Commonwealth: 'I declare before you all that my whole life, whether it be long or short, shall be devoted to your service and the service of our great imperial family to which we all belong.'
Princess Elizabeth and Philip had been married for less than five years when their lives were altered irrevocably by the death of the King on February 6, 1952, and the young royal became Queen.
Away from her public duties, the Queen's marriage to Philip has been a union that has produced four children – Prince Charles, born in 1948; Princess Anne, born in 1950; Prince Andrew, in 1960, and Prince Edward in 1964.
In 1977, record crowds greeted the monarch during her Silver Jubilee celebrations and thousands held street parties in her honour.
The Queen dubbed 1992 her 'annus horribilis' as during that year the Princess Royal divorced, the Duke and Duchess of York separated, the Prince and Princess of Wales were splitting up and Windsor Castle went up in flames.
Five years later the Queen and the monarchy faced one of its gravest crises when Diana was killed in a Paris car crash in 1997.
She was perceived as out-of-step with the feelings of mourners wondering why the Queen, who was at Balmoral with Princes William and Harry, took so long to speak publicly about the tragedy.
In 2002, the Queen suffered the tragic double blow of losing both the Queen Mother and her sister, Princess Margaret – within just weeks of one another.
It was her Golden Jubilee year, but the celebrations continued and were a resounding success, with one million people turning out to party in June on the streets of London, much like her Diamond Jubilee 10 years later.
The new millennium has been a much happier period for the Queen, with Charles marrying his long-term love, Camilla, now the Duchess of Cornwall, in 2005. And the world was left delighted by the 2011 wedding of the Duke and Duchess of Cambridge, who now have two children: Prince George and Princess Charlotte.
Now in her 10th decade, the Queen appears to be at a point where both her work and family life offer her deep contentment – and she appears set to reign over us for quite some time to come.
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