Remembrance Day in 2017 at the Cenotaph (Picture: Ministry of Defence).
What is Armistice Day?
Armistice Day, also known as Remembrance Day, marks the day the First World War ended on the 11th hour, of the 11th day, of the 11th month in 1918.
It is not to be confused with Remembrance Sunday, which falls on the second Sunday in November every year.
This year, 100 years on since the Great War ended, Remembrance Sunday and Armistice Day have fallen on the same day.
Across the UK, a two-minute silence will be held at 11am on 11 November to remember those killed in conflict.
King George V organised Britain's first two-minute silence in 1919 - exactly one year after the First World War ended.
The tradition has been continued ever since, and the fallen from every conflict have been commemorated.
What countries other than the UK observe Remembrance Day?
Armistice Day and Remembrance Sunday are not just celebrated in the UK.
Across the former British Commonwealth, many countries such as Australia, Canada, Belize and Barbados all celebrate Armistice Day on 11 November - although, the biggest day of remembrance for Australia and New Zealand is Anzac Day on 25 April.
Close to the UK, in France and Belgium Remembrance Day is a national holiday with shops, banks and businesses all closed.
There are also ceremonies, the laying of wreaths at memorials and military parades to remember the fallen.
France and Belgium also hold a one-minute silence, rather than two, at 11am to remember those killed and thank them for their sacrifice.
The United States and Poland both remember the fallen on 11 November.
The day is known as 'Independence Day' in Poland and is a public holiday, with ceremonies, church services and parades taking place like the UK.
Meanwhile, 'Veterans Day' in the US is a national holiday and has been commemorated since 1926.
However, it changed its name from 'Armistice Day' to 'Veterans Day' in 1954 after a petition urged to highlight the sacrifice made by soldiers in other wars.
Ireland holds the National Day of Commemoration on the Sunday closest to the 11 July, remembering Irish soldiers killed in all conflicts.
In Italy, soldiers killed in the Great War are remembered on 4 November, the day of the ceasefire that followed the Armistice of Villa Giusti in 1918.
Denmark, the Netherlands, Norway and Israel all have similar events at different times of the year.
Germany also holds a Remembrance Day on the Sunday closest to 16 November.
The day is called 'Volkstrauertag' and is the national day of mourning. The day is designed to remember those killed in the First World War and is also known as 'silent day', with music and dancing events banned in some states.
Do any other countries wear poppies to commemorate those who were killed in wars?
Poppies have long been a symbol of Remembrance in the UK and according to the Royal British Legion (RBL), who now sell the poppies, a Canadian doctor was the inspiration.
After losing a friend in Ypres in 1915, Lieutenant Colonel John McCrae wrote the poem 'In Flanders Fields' about the poppies growing in the battlefields.
The RBL formed in 1921 and that year they sold nine million poppies, raising £106,000 for veterans of the First World War.
While in Scotland the poppy is also still used as a symbol of remembrance, the poppies fabricated by Poppyscotland have four petals and no leaf.
However, the poppy is controversial in Northern Ireland and the Republic of Ireland. It is associated with being a British symbol in both Northern Ireland and the Republic of Ireland, which is a historically divisive issue in the two areas.
Although their poppies have a slightly different look to ours in the UK, certain Commonwealth countries such as Canada, Australia and New Zealand have also continued to use the Remembrance poppy since 1921.
Poppies are worn in New Zealand and Australia on both Remembrance Day and Anzac Day.
However, not all countries use the poppy to commemorate their fallen.
Although not as widely worn as in the UK, in France, theBleuet de France - or blue cornflower - serves as the symbol of remembrance, raising money for veterans and their families.
Other European countries such as Poland and Belgium associate the poppy with remembrance, though the tradition of wearing a poppy on Remembrance Day is observed a lot less than in the UK.