For the first time since 1973 the Queen will not be attending the Commonwealth heads of government meeting this year, Buckingham Palace has said.
She will be represented by the Prince of Wales at the summit in Sri Lanka in November.
Buckingham Palace said it was reviewing the amount of long-haul travel the Queen undertook.
The Queen, 87, is the head of the Commonwealth and every two years leaders meet to discuss global issues.
The Queen was first present at the Commonwealth heads of government meeting (Chogm) in Ottawa, Canada, in 1973 - missing the first one in 1971 - and has been at every summit since. The last one, in 2011, was held in Perth, Australia.
A Buckingham Palace spokesman said: "I can confirm the Queen will be represented by the Prince of Wales.
"The reason is that we are reviewing the amount of long-haul travel that is taken by the Queen."
BBC royal correspondent Peter Hunt said the Queen would not have taken the decision lightly and it was both surprising and significant.
He said it was a significant moment for the Prince of Wales and it was also a symbolic move.
"It is about transition, about preparing this country for an elderly head of state who will be able to do less and less," he said.
"There is no intention of abdication. It will just not happen during her reign. It is the palace addressing the practicalities of her advancing age - you will see less of her and more of him."
It is expected that Prince Charles will be joined by the Duchess of Cornwall at the summit in the Sri Lankan capital Colombo, he added.
By stepping in for the Queen, Prince Charles will be performing one of his most significant duties to date as a future King.
He has never before attended in place of the monarch at the two-yearly gathering of Commonwealth leaders. In 2007, both the Prince and the Queen attended Chogm in Uganda.
Prime Minister David Cameron said the Queen's decision was "entirely understandable" and did not reflect any decrease in her commitment to the Commonwealth.
He said: "I think we should all pay tribute to the incredible work that Her Majesty has done over six decades in support of the Commonwealth. I know that she is as passionate about the Commonwealth today as she has ever been."
The Queen was forced to cancel her appearance in March at the Commonwealth Day service at Westminster Abbey, the first time the monarch had missed the occasion in 20 years.
It was one of a number of engagements she cancelled after being admitted to hospital suffering from the symptoms of gastroenteritis.
The Queen is the Commonwealth's symbolic head and has no formal powers over the 54 countries and two billion citizens which make up the voluntary association.
Commonwealth Secretary General Kamalesh Sharma said the "family of nations completely understands and respects" the Queen's decision.
"The presence of the Prince of Wales at our Commonwealth gathering will carry forward Her Majesty's outstanding record of enduring commitment and diligent service as head of the Commonwealth," he said.
Concerns have been raised about the choice of Sri Lanka as the host nation for the 2013 summit.
Campaigners including Amnesty International are calling for the Chogm meeting not to take place there before an investigation is carried out into human rights abuses in the final six months of the 26-year Sri Lankan civil war.
Britain is facing pressure to lead a boycott of the meeting, with Canada's government indicating it will not attend unless specific criteria are met.
Shadow foreign secretary Douglas Alexander said he hoped Mr Cameron would "think again" about his decision to attend the summit "given the very serious and continuing allegations in relation to human rights".
He told Channel 4 News: "I think he should be using the coming months between now and November to be very clear to the Sri Lankans that unless we see substantive change then he, along with the Canadian and other governments, I hope, will give very serious consideration to boycotting this summit."
Buckingham Palace said the Queen's decision was not related to the political situation.
"The key point here is that the Queen will be represented, although she is not there in person, by the Prince of Wales," a spokesman said.