Queen Elizabeth is celebrating the 60th anniversary of her accession to the throne.
In her message marking the event on Monday, the Queen says she is dedicating herself "anew to your service" and says she is deeply moved by the support shown for her Diamond Jubilee.
"I am writing to thank you for the wonderful support and encouragement that you have given to me and Prince Philip over these years and to tell you how deeply moved we have been to receive so many kind messages about the Diamond Jubilee."
The Queen's great-great grandmother, Queen Victoria, is the only other British monarch to achieve the milestone.
Accession Day on 6 February is always tinged with sadness for the monarch as it marks the day her father died in 1952 as well as the date of her accession to the throne.
She usually spends the day privately but, this year, has engagements planned.
She will visit King's Lynn Town Hall and a nearby infant and nursery school.
A big crowd is expected, despite the cold weather.
On the eve of the anniversary, the Queen and Prince Philip joined the congregation at West Newton Church in the monarch's private Sandringham estate in Norfolk.
Programme of events to celebrate reign of 60 years
Two official photographs are being released and a 41-gun salute will be held in Hyde Park in London, followed by a 62-gun salute at the Tower of London on the banks of the River Thames to mark the occasion
The milestone will also be marked by several events in the coming months, with the main celebrations taking place in June, the BBC reports
These include the Queen leading a flotilla of 1000 boats along the Thames and a chain of beacons lit across the country.
Palace officials say the Queen has asked there should be no unnecessary spending of public money on the Diamond Jubilee celebrations.
This week also marks 200 years since the birth of novelist Charles Dickens and the event is being marked with festivities throughout the United Kingdom.