The UK fell silent in tribute to service personnel who have died during conflicts, as part of the annual Remembrance Sunday service.
A two-minute silence was observed, before the Queen laid the first wreath at the Cenotaph in central London.
More than 10,000 military veterans and civilian representatives marched past the monument.
Services also took place at memorials across the UK, in Commonwealth countries and at bases abroad.
The crowds gathered in central London stood quietly as Big Ben struck 11:00 GMT.
The beginning and end of the silence was marked with the firing of a round by the King's Troop Royal Horse Artillery, using a 13-pounder World War One gun.
The monarch then laid her wreath at the foot of the monument, the focal point of the UK's Remembrance Sunday events since World War One, bowing her head after paying her respects.
On a sunny but crisp autumn day, the Duke of Edinburgh, the Duke of Cambridge and Prince Harry laid wreaths.
Prime Minister David Cameron was next to pay his respects, followed by Labour leader Ed Miliband and Deputy Prime Minister Nick Clegg.
Former prime ministers Sir John Major, Tony Blair and Gordon Brown, along with London Mayor Boris Johnson, also took part in the ceremony, as did military and emergency service chiefs and representatives from Commonwealth countries.
The assembled marchers - who for the first time included representatives of a World War Two unit known as "Churchill's Secret Army" - then set off down Whitehall.
In events elsewhere:
- In Scotland, First Minister Alex Salmond and Scottish Secretary Alistair Carmichael laid wreaths at St Giles Cathedral in Edinburgh
- In Wales, the main event took place at Cardiff's Welsh National War Memorial
- Ireland's Taoiseach Enda Kenny laid a laurel wreath at the memorial in Enniskillen, while in Belfast, Stormont First Minister Peter Robinson, Northern Ireland Secretary Theresa Villiers and Ireland's deputy leader, Tanaiste Eamon Gilmore, attended a ceremony
- Some of the largest gatherings outside London took place in Birmingham, York, Portsmouth and Bristol
- At Camp Bastion, in Helmand Province, a service was held to remember the 446 servicemen killed in the 11 years of conflict in Afghanistan. Wreaths were laid by the Duke of York and Defence Secretary Philip Hammond
- The Prince of Wales and the Duchess of Cornwall marked the event during their official tour of India, joining the congregation of a Mumbai church for their annual remembrance service and meeting some of India's last surviving World War Two veterans
- Meanwhile, police issued an appeal after World War One medals were stolen from a Nottinghamshire house, a day before Remembrance Sunday
Among those who marched past the Cenotaph for the first time, were 41 members of the British Resistance Movement - known as Churchill's Secret Army or the Coleshill Auxiliaries - volunteer fighters charged with going underground to continue the fight in the event of a German invasion of Britain in World War Two.
John Brunel Cohen, a D-Day veteran, was among those who gathered in London.
"The whole parade is very thought provoking, evocative and emotive," he said. "To march through the streets of London cheered by thousands is an experience however often you've done it."
Col Matt Jackson, who was attending his first service at the Cenotaph, said the experience was "hugely humbling".
"During the two-minute silence, you could see the thought process behind everybody about what they were doing and the remembrance and what it obviously meant to a number of individuals," he said.
"You couldn't hear a thing, other than the leaves in the background."
Kerry Ashworth, whose son James was killed in Afghanistan last year and was posthumously awarded the Victoria Cross for bravery, said it was a special day.
"The job that they do is so hard and so tough and when somebody loses their life, it's just one little thing that you can do just to remember them for a few minutes," she said.