As Prince Harry arrives in the United States to begin a seven-day tour, we look back at other royal visits to the country.
The Queen will be joined by members of both Houses for the State Opening of Parliament today.
The Queen will miss the Commonwealth summit for the first time in 40 years as part of a review of her long-haul travel.
The Queen will go ahead with a pre-planned visit to Woolwich Barracks next Friday despite the recent attack on soldier Lee Rigby, Buckingham Palace has announced.
She will present medals and meet the families of soldiers serving in Afghanistan.
Her visit will also include several military displays, a chance to view horses being treated in the veterinary clinic and a private lunch in the Sergeants' Mess.
– Buckingham Palace spokesperson
The Queen is of course concerned by the report of an attack in Woolwich earlier today. Her Majesty is being kept informed.
The spokesperson also confirmed the Queen will visit the King's Troop Royal Horse Artillery at Woolwich barracks on 31st May, which was planned before today's attack.
In a message of condolence to US president Barack Obama, the Queen said:
I was deeply saddened to hear of the loss of life and devastation caused by yesterday's tornado in Oklahoma.
Prince Philip joins me in offering our heartfelt condolences to the victims and their families at this difficult time.
Our deepest sympathies go out to all those whose lives have been affected, as well as the American people.
The Queen met members of a lifeboat crew and admired the RNLB The Princess Royal during a visit to St Ives RNLI in Cornwall.
Hundreds of well-wishers cheered and waved in the Cornish sunshine to welcome the Queen and Duke of Edinburgh.
The Queen, wearing a lilac coat and matching hat with a black patent handbag and court shoes, and Philip, in a dark suit and gold tie, arrived at St Erth station on the Royal Train before transferring to a scheduled service to St Ives.
They were then taken by car to St Ives RNLI, where they were greeted at 10.40am by hundreds of locals who lined the seafront.
This year marks the 70th year of the Queen attending the State Opening of Parliament.
Queen Elizabeth began attending with her father before she became Queen in 1943.
During this time there has been two occasions where the Queen did not attend, the first when she was pregnant with Prince Andrew, and the second when pregnant with Prince Edward.
The Queen's decision not to go to Sri Lanka for the Commonwealth Heads of Government Meeting is a significant signal of an increasing role for Prince Charles and the younger royals.
The decision suggests the Queen is unlikely to do much long-haul travel from now on. A Republic campaign group calls it "succession by stealth".