The Queen sees royal visits as an important part of her duties
The Queen has cancelled a state visit because of "other commitments", not her age or the Duke of Edinburgh's health, Buckingham Palace has said.
The location of the visit has not been disclosed, but officials insist that Prince Philip's recent back injury is not the reason.
The 87-year-old prince has had to cancel three engagements this year.
The Queen last cancelled a tour after the 9/11 attacks and then two years later during the 2003 Iraq War.
According to the BBC's royal correspondent Peter Hunt, this time the Queen has taken the unusual step of cancelling because "there is just too much on".
Immediately after the abandoned trip, the Queen is due to receive the president of Mexico, while world leaders are due in London to discuss the global financial crisis.
In 2001, the Queen had been due to carry out a 16-day tour of Australia and New Zealand, which would have coincided with a Commonwealth Heads of Government meeting in Brisbane.
But the attacks on New York on 11 September meant that gathering was postponed as leaders focused on security concerns.
The Queen's trip did go ahead in February 2002, when she toured the two countries before opening the rescheduled Commonwealth meeting.
In 2003, a planned state visit to Belgium was cancelled because of the looming war in Iraq.
That time the decision was based on advice from Downing Street.
A full state tour to Belgium was not rescheduled, but the Queen carried out an official visit in July 2007 to mark the 90th anniversary of the battle of Passchendaele.
Our correspondent adds that the Queen views state visits as one of her most important duties - as it gives her a chance to fly the flag and promote UK businesses.