The poppy has been a symbol of Remembrance for the last century.
It is designed to serve as a simple reminder of those who gave their lives in the war.
The symbol stems from the poppies that grew on the battlefield after the end of the First World War, as described in the poem 'In Flanders Fields'.
The poppy has since grown to represent not just those who sacrificed their lives in the Great War, but all those who have died during later conflicts.
The money raised by the Poppy Appeal is used to help current servicemen and women, whose lives have been changed by wars that they fought in.
When did the tradition start?
The Royal British Legion first sold poppies in 1921.
They sold out almost straight away and raised more than £100,000 for the those who had been affected by the war.
In 1922 a factory was set up, where disabled soldiers were employed to make the poppies.
This factory is still running and produces millions of poppies every year.
What is the etiquette?
There is no definitive answer to this.
Some say the poppy should be worn from 31 October, while others say you should wear it in the 11 days leading up to Remembrance Day.
Some believe they should not be worn until after Bonfire Night.
The positioning of the poppy can also cause some confusion.
Many say the poppy should be worn on one's left to be close to the heart, as well as the side of military medals.
Others say men should wear it on the left and women on the right, just like the Queen.
The Royal British Legion, however, has previously told the BBC: "There is no right or wrong way to wear a poppy.
"It is a matter of personal choice whether an individual chooses to wear a poppy and also how they choose to wear it.
"The best way to wear a poppy is to wear it with pride."
Wearing the poppy in the military
According to UK military dress regulations, all ranks are authorised to wear a poppy from the launch of the Poppy Appeal, up until Armistice Day on 11 November.
The British Army's standards dictate that: "In all parade orders of dress the fabric poppy is to be worn behind the left-hand button of the No 1 Dress cap.
"If wearing the great coat it is to be worn in the top [left-hand] button hole of the coat.
"In Barrack Dress and Combat Dress, the poppy is to be pinned to the left breast.
"If an individual is inside wearing one of the parade orders of dress and wishes to be seen to be wearing a poppy, one may be pinned to the left breast above the medals or medal ribbons.
"This poppy is to be removed if the individual then moves outside and has one in the cap so that two poppies are not worn at the same time.
"It is to be noted that a poppy is not worn in Mess Dress except on the cap.
"An enamelled poppy no larger than 3cm and in the style shown can be worn in place of the fabric poppy in Barrack and Combat Dress only.
"It is to be pinned to the left breast of the jersey or to the centre of the left breast pocket flap in Combat Dress."
The Ministry of Defence has confirmed in the past that wearing the poppy, however, is not obligatory.
During the National Service of Remembrance at the Cenotaph on Remembrance Sunday, personnel on parade do not wear a poppy as it is not a part of their formal uniform.
The service chiefs in attendance do.
Cover image: Royal Navy.