Ceremonies have taken place across the UK to remember the servicemen and women who lost their lives in all past and current armed conflicts.
The Queen led Remembrance Sunday tributes at the Cenotaph in London's Whitehall before thousands of veterans marched past the memorial.
Troops on active service in Iraq and Afghanistan also held services.
This year's events come just two days before the 90th anniversary of the armistice at the end of World War I.
The commemoration of Britain's war dead began with a gun blast and two minutes' silence on Whitehall. The Queen then laid the first wreath of poppies.
She was followed by the Duke of Edinburgh, the Prince of Wales and other members of the Royal family.
Prime Minister Gordon Brown, Foreign Secretary David Miliband, opposition party leaders and Commonwealth envoys also laid wreaths.
For the first time, the Territorial Army - which is celebrating its 100th anniversary - laid a wreath at the monument.
Royal British Legion spokesman Stuart Gendall said it was important for the nation to come together and remember all those that died fighting for their country.
Remembrance services were also held at Glasgow's George Square and Belfast's City Hall.
Scotland's First Minister Alex Salmond laid a wreath at the Stone of Remembrance in Edinburgh and said this was a time to "pause for thought".
At the Welsh National War Memorial in Cathays Park, Cardiff, First Minister Rhodri Morgan paid tribute to the sacrifices made by members of the armed forces.
Des Feely, the father of the first female British soldier killed in Afghanistan, was due to lay a wreath in her honour at a ceremony in Carlisle's city centre.
Corporal Sarah Bryant, 26, was killed on duty in June in a roadside explosion near Lashkar Gah, in the south of the country.
Mr Feely said: "I felt it was quite an honour to do this on Sarah's behalf and on behalf of all the soldiers that have been killed.
"It's important to keep remembering, and it's not just limited to the First or Second World War. There are ongoing sustained casualties in Iraq and Afghanistan.
"It highlights the fact that for people here in this country, their way of life - freedom of speech, freedom of movement - is still being preserved through the actions of others."
In Somerset, Harry Patch, Britain's last living veteran of the First World War trenches, laid a wreath in honour of his fallen comrades.
"It was 90 years ago. But you can't forget it," said the 110 year old.
On the other side of the country, a lone Spitfire flew over Duxford near Cambridge, home to one of England's most famous Battle of Britain air bases.
In the Essex garrison town of Colchester, thousands gathered to salute the war dead, turning out in higher numbers than last year.
The Colchester-based 2nd Battalion, The Parachute Regiment, lost nine soldiers during its recent tour of Afghanistan, plus a further six linked to it.
'Pause and reflect'
A Remembrance Day ceremony has already taken place in Afghanistan's largest military base, in Kandahar.
About 2,000 British servicemen and women are stationed there.
The BBC's Ian Pannell in Afghanistan said in the 12 months since the last Remembrance Sunday service, 39 British men and women have died while serving their country.
Of the personnel at the service, he said: "This really was a time for them to pause and reflect. There was the last call; there were two minutes of silence. There were a number of hymns and also prayers delivered to those who lost their lives."
Harry Patch, accompanied by Henry Allingham, 112, and Bill Stone, 108 - the three remaining First World War veterans who still live in the UK - are due to mark the two-minute silence at the Cenotaph to commemorate Armistice Day on Tuesday.