The Queen will honour hundreds of high-achieving Scouts at Windsor Castle later on Sunday.
Accompanied by the Duke of Edinburgh, the Queen, who is patron of the Scout Association, will conduct the "review" of the Scouts, presenting the Queen's Scouting Award to 600 youngsters from the UK and around the Commonwealth.
The award is the highest a Scout can achieve.
To land it, Scouts need to fulfil many requirements, including working in the local community for 18 months and completing a four-day expedition.
Normally the review involves only UK Scouts but this year the Queen will meet youngsters from as far afield as Uganda, Belize and St Lucia, organisers said.
She will be met by adventurer and television star Bear Grylls, who is Chief Scout, and he will present UK chief commissioner Wayne Bulpitt and chief executive Derek Twine.
Meanwhile it's been revealed that a Kenyan hotel the Queen was staying at when she acceded to the throne will be among the locations where beacons will be lit to mark her Diamond Jubilee.
The Treetops Hotel in the Aberdare national park became known for its royal connection after George VI died while his daughter, then Princess Elizabeth, was staying there in 1952.
A beacon will be lit at the hotel on June 4 as part of a network of Diamond Jubilee Beacons across the UK, the Channel Islands, Isle of Man, Commonwealth and overseas territories.
The Queen will light the National Beacon on the Mall in London.
Pageant-master Bruno Peek said: "I am delighted that the government of Kenya has agreed to light a beacon in such an historic location as part of this unique event and I applaud them for their initiative."