But there are other coloured poppies too - purple, black and white - that have different meanings.
The red poppy is the most famous symbol used to commemorate those who sacrificed their lives in World War One and conflicts that followed.
Wearing a poppy was inspired by the fields of poppies that grew where many of the battles were fought.
The red poppy is connected to the Royal British Legion - a charity created by veterans of World War One.
They say that the red poppy represents remembrance and hope.
The purple poppy is often worn to remember animals that have been victims of war.
Animals like horses, dogs and pigeons were often drafted into the war effort, and those that wear the purple poppy feel their service should be seen as equal to that of human service.
In particular, many horses were killed or injured in World War One.
Donations to the Purple Poppy Appeal, which is organised by the War Horse Memorial, will go to charities like World Horse Welfare and the animal charity, Blue Cross.
The black poppy has two different meanings attached to it.
It is most commonly associated with the commemoration of black, African and Caribbean communities' contribution to the war effort - as servicemen and servicewomen, and as civilians.
The campaign organisers say that while they also support the red poppy, they feel that the black poppy highlights this contribution and the place of black, African and Caribbean communities in remembrance.
Some people feel that the red poppy glorifies war and conflict.
Instead they might choose to wear a white poppy.
The white poppy is handed out by a charity called Peace Pledge Union, which promotes peace.
They say that the white poppy commemorates people who died in conflict, but focuses on achieving peace and challenging the way we look at war.
What poppy do you wear? Or do you choose not to wear a poppy? Let us know in the comments below.