Three days of events to mark the Queen's official 90th birthday will begin on Friday with a thanksgiving service at St Paul's Cathedral.
The Queen and the Duke of Edinburgh, who turns 95 today, will be joined by other members of the Royal family, former Prime Ministers and several dignitaries.
Readers at the service will include David Cameron and Sir David Attenborough, who is the same age as the Queen.
It will be followed by a lunch for the Governors General of all Commonwealth Realms at Buckingham Palace.
At midday there will be a gun salute at Hyde Park by the King's Troop Royal Horse Artillery in honour of Prince Philip's birthday followed by a 1pm salute at the Tower of London by the City of London's Reserve Army Regiment.
On Saturday, events will include the annual Trooping the Colour ceremony on Horse Guards Parade, followed by an RAF flypast of 29 aircraft and a flotilla of 50 vessels processing down the Thames.
The celebrations will culminate on Sunday with a party on The Mall for 10,000 people from over 600 organisations of which the Queen is Patron.
Ahead of the weekend of celebration Buckingham Palace released a new portrait of the Queen with the Duke of Edinburgh.
Wearing matching pale pink, the couple, who have been married for more than 68 years, sit side by side as they smile for the camera.
It is the sixth and final picture in a series of portraits taken by photographer Annie Leibovitz to mark the Queen's birthday milestone.
Events to mark the Queen's birthday this weekend:
- National Service of Thanksgiving at St Paul's Cathedral
- Governors-General lunch at Buckingham Palace
- Flotilla of 50 vessels processing down the Thames
- 62-gun salute at the Tower of London
- Annual Trooping of the Colour ceremony
- RAF flypast of 29 aircraft
- Patrons lunch, picnic on the Mall for 10,000 people