The History behind wearing the Poppy on Remembrance Day

The tradition of wearing a poppy on Remembrance Day stems directly from the poem "In Flanders Fields" by John McCrea.
Lieutenant Colonel John McCrea was a Canadian physician, whom at the time was located at, what is now, the Common Wealth War Graves Essex Farm situated just north of Ypres (Iepre in Flemish), Belgium during the First World War

the field dressing station at Essex Farm

On the 22nd April 1915 the Germans launched the 2nd Battle of Ypres with a gas attack. This was the first time that gas had been used as a weapon.
During the battle McCrae was running a Field Dressing Station on the main road between Ieper and Boezinge. The local farm had been nicknamed Essex Farm and it was this name that was eventually to be given to the cemetery, which had grown up alongside the Dressing Station.
As the battle reached its height with the secondary attacks against the Canadian positions, the Field Dressing Station ended up even closer to the front line.
On the 3rd May 1915 McCrae composed one of the most famous and popular poems to come from the war, in response to the death of his friend the day before.

'In Flanders Fields'

In Flanders fields the poppies blow

Between the crosses, row on row,

That mark our place; and in the sky

The larks, still bravely singing, fly

Scarce heard amid the guns below.

We are the Dead. Short days ago

We lived, felt dawn, saw sunset glow,

Loved and were loved, and now we lie

In Flanders fields.

Take up our quarrel with the foe:

To you from failing hands we throw

The torch; be yours to hold it high.

If ye break faith with us who die

We shall not sleep, though poppies grow

In Flanders fields.

Essex Farm Cemetery monument to John McCrea

John McCrea died suddenly on January 28th 1918 in France in a British Field Army Hospital from a self-diagnosed case of pneumonia, brought on from chronic asthma and the lingering effects of the German gas attack. He is buried in the Wimereux Communal Cemetery, just south of Calais on the coast of France

In 1918 Moina Michael, an American war secretary with the YMCA, was deeply moved by McCrae's work and it was she who first wore a poppy as act of keeping the faith. Others that she had bought she sold to friends, giving the money to Servicemen in need.
In 1920 Madame Guerin from the French YMCA, inspired by this idea, suggested that artificial poppies should be made and sold to help ex-Servicemen and their dependants.
The idea of mass producing poppies and selling them as a charity was put to Field Marshal Earl Haig in 1921 and he agreed with the idea. Thus the Royal British Legion's annual Poppy Day was brought into being and so too for the veterans groups throughout the Commonwealth.