The Battle of Agincourt ( AJ-in-kor(t); French: Azincourt [azku]) was an English victory in the Hundred Years' War. It took place on 25 October 1415 (Saint Crispin's Day) near Azincourt, in northern France. The unexpected English victory against the numerically superior French army boosted English morale and prestige, crippled France and started a new period of English dominance in the war that would last for 14 years until France defeated England in the Siege of Orlans in 1429.

After several decades of relative peace, the English had resumed the war in 1415 amid the failure of negotiations with the French. In the ensuing campaign, many soldiers died from disease, and the English numbers dwindled; they tried to withdraw to English-held Calais but found their path blocked by a considerably larger French army. Despite the numerical disadvantage, the battle ended in an overwhelming victory for the English.

King Henry V of England led his troops into battle and participated in hand-to-hand fighting. King Charles VI of France did not command the French army as he suffered from psychotic illnesses and associated mental incapacity. The French were commanded by Constable Charles d'Albret and various prominent French noblemen of the Armagnac party. This battle is notable for the use of the English longbow in very large numbers, with the English and Welsh archers comprising nearly 80 percent of Henry's army.

The Battle of Agincourt is one of England's most celebrated victories and was one of the most important English triumphs in the Hundred Years' War, along with the Battle of Crcy (1346) and Battle of Poitiers (1356). It forms the backdrop to events in William Shakespeare's play Henry V, written in 1599.

The Hundred Years' War (French: La guerre de Cent Ans; Picard: Dgère d'Un Chint Ans; 1337–1453) was a series of armed conflicts between the kingdoms of England and France during the Late Middle Ages. It originated from disputed claims to the French throne between the English royal House of Plantagenet and the French royal House of Valois. Over time, the war grew into a broader power struggle involving factions from across Western Europe, fueled by emerging nationalism on both sides.

The Hundred Years' War was one of the most significant conflicts of the Middle Ages. For 116 years, interrupted by several truces, five generations of kings from two rival dynasties fought for the throne of the largest kingdom in Western Europe. The war's effect on European history was lasting. Both sides produced innovations in military technology and tactics, including professional standing armies and artillery, that permanently changed warfare in Europe; chivalry, which had reached its height during the conflict, subsequently declined. Stronger national identities took root in both countries, which became more centralised and gradually rose as global powers.The term "Hundred Years' War" was adopted by later historians as a historiographical periodisation to encompass related conflicts, constructing the longest military conflict in European history. The war is commonly divided into three phases separated by truces: the Edwardian War (1337–1360), the Caroline War (1369–1389), and the Lancastrian War (1415–1453). Each side drew many allies into the conflict, with English forces initially prevailing; the House of Valois ultimately retained control over France, with the previously-intertwined French and English monarchies thereafter remaining separate.