Services were held across Scotland, including a gathering at the Cenotaph in Glasgow's George Square and the Stone of Remembrance in Edinburgh, where First Minister Alex Salmond and Scottish Secretary Michael Moore both laid wreaths.
The First Minister then attended a Service of Remembrance at St Giles' Cathedral.
He said: "Today presents every man, woman and child in Scotland with the opportunity to pause and reflect on the immense sacrifice which so many have made to protect our way of life and freedom down the years.
"This moment allows us to pay tribute to all of our servicemen and women, past and present, who have laid down their lives in defence of our country and whose sacrifice will never be forgotten.
"It is important that we also remember that today's commemoration is not simply about historical events but also about the sacrifices servicemen and women today continue to make."
Thousands of people gathered in Glasgow's George Square to pay their respects to fallen soldiers on Remembrance Sunday.
The service held at the Cenotaph saw over a thousand serving soldiers, veterans, cadets, police and firemen on parade, along with Royal British Legion and Remembrance Day service party which included Lord Lieutenant and Lord Provost of Glasgow Sadie Docherty and Deputy First Minister Nicola Sturgeon.
A Guard of Honour was provided by The Royal Air Force, Lossiemouth, with music by the 6th Battalion of the Royal Regiment of Scotland.
At the Cenotaph memorial in London, the monarch laid the first wreath to commemorate members of the Armed Forces who died fighting in all conflicts since the First World War.
In brilliant autumn sunshine, senior members of the monarchy joined Prime Minister David Cameron, military chiefs, servicemen and women and thousands of watching spectators in paying their respects.
When the first stroke of eleven sounded from nearby Big Ben, Whitehall observed a two-minute silence only punctuated by the hum of distant London traffic and birds.
The Queen laid the first wreath, followed by the Duke of Edinburgh. Then the Duke of Cambridge, wearing his RAF uniform, laid a wreath, under the gaze of the Duchess of Cambridge, who watched from a balcony at the Foreign Office alongside the Countess of Wessex and the Princess Royal's husband Vice Admiral Sir Timothy Lawrence.
William was followed by the Duke of York, the Earl of Wessex, the Princess Royal, Prince Michael of Kent and Field Marshal Lord Guthrie of Craigiebank.
Wreaths were also laid by Mr Cameron, Liberal Democrat leader Nick Clegg, opposition leader Ed Miliband and Westminster Plaid Cymru group leader Elfyn Llwyd, as well as high commissioners from Commonwealth countries and leaders of the Armed Forces.
Veterans' representatives laid wreaths at the Cenotaph before almost 10,000 ex-servicemen and women marched past to commemorate their fallen comrades.
This year's Remembrance commemoration is the first to take place since the death of the last veteran to serve during the First World War on either side, according to the Royal British Legion.
There was warm applause from the crowd as the parade marched past the giant war memorial, inscribed to The Glorious Dead.
Earlier, the Prince of Wales and Duchess of Cornwall attended a ceremony in Auckland as part of their Jubilee tour of New Zealand.
Under grey skies the royals sat with New Zealand's prime minister John Key, veterans from across the decades, and members of the public around the Auckland Cenotaph.
The Duke of Kent was also overseas, representing the Queen at a service in the Falkland Islands.
In Northern Ireland, the prime minister of the Republic of Ireland Taoiseach Enda Kenny attended the remembrance service in Enniskillen.
The symbolic visit came as the Co Fermanagh town marked the 25th anniversary of the IRA Poppy Day bomb attack, which claimed the lives of 12 people.
Mr Kenny laid a laurel wreath at the cenotaph, only yards from where the no-warning blast detonated a quarter of a century ago.
Thousands of people also respected the two-minute silence on Twitter, abstaining from posting messages during the period of reflection. The idea was spread using the hashtag #2minutesilence.