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.