A remembrance poppy is an artificial flower worn in some countries to commemorate their military personnel who died in war. Remembrance poppies are produced by veterans' associations, which exchange the poppies for charitable donations used to give financial and practical support to members and veterans of the armed forces.

Inspired by the war poem "In Flanders Fields" and promoted by Moina Michael, they were first used near the end of World War I to commemorate British Empire and United States military casualties of the war. Anna Guérin established the first "Poppy Days" to raise funds for veterans, widows, orphans and liberty bonds, as well as charities such as the Red Cross.

Remembrance poppies are most commonly worn in Commonwealth countries, where the symbol has been trademarked by veterans' associations for fundraising. Remembrance poppies in Commonwealth countries are often worn on clothing in the weeks leading up to Remembrance Day, with poppy wreaths also being laid at war memorials on that day. However, in New Zealand, remembrance poppies are most commonly worn on Anzac Day.

The red remembrance poppy has inspired the design of several other commemorative poppies that observe different aspects of war and peace. In France, a bleuet de France is worn instead of a remembrance poppy to commemorate military personnel who died in war.

References to war and poppies in Flanders can be found as early as the 19th century, in the book The Scottish Soldiers of Fortune by James Grant:

The Scots in Holland and Flanders: At Neerwinden, in 1693, the brigade again suffered heavy loss, and William was compelled again to give way before the white-coated infantry of France with the loss of 10,000 men. "During many months after", wrote the Earl of Perth to his sister (as quoted by Macaulay), "the ground was strewn with skulls and bones of horses and men, and with fragments of hats, shoes, saddles, and holsters. The next summer the soil, fertilised by 20,000 corpses, broke forth into millions of scarlet poppies."

The opening lines of the World War I poem "In Flanders Fields" refer to Flanders poppies growing among the graves of war victims in a region of Belgium. The poem is written from the point of view of the fallen soldiers and in its last verse, the soldiers call on the living to continue the conflict. The poem was written by Canadian physician John McCrae on 3 May 1915 after witnessing the death of his friend and fellow soldier the day before. The poem was first published on 8 December 1915 in the London-based magazine Punch.

Moina Michael, who had taken leave from her professorship at the University of Georgia to be a volunteer worker for the American YMCA Overseas War Secretaries Organization, was inspired by the poem. She published a poem of her own called "We Shall Keep the Faith" in 1918. In tribute to McCrae's poem, she vowed to always wear a red poppy as a symbol of remembrance for those who fought in and assisted with the war. At a November 1918 YMCA Overseas War Secretaries' conference, she appeared with a silk poppy pinned to her coat and distributed twenty-five more poppies to attendees. She then campaigned to have the poppy adopted as a national symbol of remembrance.