Thousands of war veterans have marched past the Cenotaph memorial in London to mark Remembrance Sunday.
After the commemoration of Britain's war dead began, with a gun blast and two minutes' silence on Whitehall, the Queen laid the first wreath of poppies.
Senior Royals followed suit, including Prince William for the first time, then the PM and other leading politicians.
Other remembrance events also took place around the country and in Afghanistan and Iraq.
This year Remembrance Sunday fell exactly 89 years after the ending of World War I, Armistice Day.
Britain's oldest war veteran, 111-year-old Henry Allingham, laid a wreath in St Omer, northern France.
At the London ceremony thousands of veterans, many elderly and frail, marched past the memorial in Whitehall to pay their respects.
Their participation began after the Queen, accompanied by the Duke of Edinburgh, Prince Charles, Prince William, the Duke of York, the Princess Royal and the Duke of Kent, had laid her wreath.
Princes Charles and Andrew and Princess Anne also laid wreaths, as did Edward for the first time.
A Clarence House spokeswoman said Prince Harry would be attending a private remembrance service with his regiment.
Gordan Brown said people would be remembering those who died in various wars.
"The sacrifice, the courage, the dedication of our armed forces is what is uppermost in our minds this weekend," he told Sky News.
"As a nation we are remembering more than perhaps 10 years ago, 20 years ago, just how much we owe to people who give their lives - and young lives - for the service of our country."
Among many to lay wreaths around the Cenotaph were Conservative leader David Cameron, acting leader of the Liberal Democrats Vince Cable, Foreign Secretary David Miliband, Democratic Unionist Party leader Ian Paisley and the Scottish National Party's leader at Westminster, Angus Robertson.
Former prime ministers Tony Blair, Baroness Thatcher and Sir John Major, also paid their respects.
More than 40 High Commissioners of Commonwealth countries also laid wreaths at the event, and the ceremony was led by the bishop of London, Richard Chartres.
Scotland's First Minister Alex Salmond earlier took part in a special Remembrance service in Sri Lanka.
In Afghanistan, 100 Royal Marines from 40 Commando earlier held a service overlooking the Kajaki dam in Helmand province, a site they have been fighting to protect from the Taleban.
At 1100 local time - 0630 GMT - a two-minute silence was held. This was followed by the laying of a single wreath at the foot of a wooden cross by the youngest marine present - Robert Worth, who turned 18 two days before he was deployed.
And, with 42 British soldiers having died since the last Remembrance Day, a roll of honour was read out.
Chris Simpkins, the Royal British Legion's director general, said Remembrance Sunday was one of the most important days in the nation's calendar.
He called on everyone to remember not only those who died in the two world wars, but also those currently fighting in the Middle East.
Elsewhere, 200 veterans of the Falklands War returned to the islands for a service of commemoration in Port Stanley.
Henry Allingham, 111, is the oldest surviving veteran of World War I.
British soldiers in Iraq and other countries also held services and parades.
The Chief of the Defence staff, Air Chief Marshall Sir Jock Stirrup, sent a message to members of the armed forces.
"For the great many of you who have served or are serving in Iraq and Afghanistan, the memories of the price paid will be all too fresh," he said.
"We have lost friends and comrades. Families have lost husbands, wives, sons, daughters, parents.
"We remember those families today; they bear a heavy burden, and the nation owes them a debt that it can never fully repay."