The Christmas truce (German: Weihnachtsfrieden; French: Trêve de Noël; Dutch: Kerstbestand) was a series of widespread unofficial ceasefires mainly along the Western Front of the First World War around Christmas 1914.

The truce occurred five months after hostilities had begun. Lulls occurred in the fighting as armies ran out of men and munitions and commanders reconsidered their strategies following the stalemate of the Race to the Sea and the indecisive result of the First Battle of Ypres. In the week leading up to 25 December, French, German, and British soldiers crossed trenches to exchange seasonal greetings and talk. In some areas, men from both sides ventured into no man's land on Christmas Eve and Christmas Day to mingle and exchange food and souvenirs. There were joint burial ceremonies and prisoner swaps, while several meetings ended in carolling. Hostilities continued in some sectors, while in others the sides settled on little more than arrangements to recover bodies.

The following year, a few units arranged ceasefires, but the truces were not nearly as widespread as in 1914; this was, in part, due to strongly worded orders from commanders, prohibiting truces. Subsequently, soldiers themselves became less amenable to truce by 1916; the war had become increasingly bitter after the human losses suffered during the battles of 1915.

The truces were not unique to the Christmas period and reflected a mood of "live and let live", where infantry close together would stop fighting and fraternise, engaging in conversation. In some sectors, there were occasional ceasefires to allow soldiers to go between the lines and recover wounded or dead comrades; in others, there was a tacit agreement not to shoot while men rested, exercised or worked in view of the enemy. The Christmas truces were particularly significant due to the number of men involved and the level of their participation—even in quiet sectors, dozens of men openly congregating in daylight was remarkable—and are often seen as a symbolic moment of peace and humanity amidst one of the most violent conflicts in human history.

During the first eight weeks of World War I, French and British troops stopped the German attack through Belgium into France outside Paris at the First Battle of the Marne in early September 1914. The Germans fell back to the Aisne valley, where they dug in. In the First Battle of the Aisne, the Franco–British attacks were repulsed and both sides began digging trenches to economise on manpower and use the surplus to outflank, to the north, their opponents. In the Race to the Sea, the two sides made reciprocal outflanking manoeuvres and after several weeks, during which the British forces were withdrawn from the Aisne and sent north to Flanders, both sides ran out of room. By November, armies had built continuous lines of trenches running from the North Sea to the Swiss frontier.

Before Christmas 1914, there were several peace initiatives. The Open Christmas Letter was a public message for peace addressed "To the Women of Germany and Austria", signed by a group of 101 British women's suffragettes at the end of 1914. Pope Benedict XV, on 7 December 1914, had begged for an official truce between the warring governments. He asked "that the guns may fall silent at least upon the night the angels sang", which was refused by both sides.

Fraternisation—peaceful and sometimes friendly interactions between opposing forces—was a regular feature in quiet sectors of the Western Front. In some areas, both sides would refrain from aggressive behaviour, while in other cases it extended to regular conversation or even visits from one trench to another. On the Eastern Front, Fritz Kreisler reported incidents of spontaneous truces and fraternisation between the Austro-Hungarians and Russians in the first few weeks of the war.

Truces between British and German units can be dated to early November 1914, around the time that the war of manoeuvre ended. Rations were brought up to the front line after dusk and soldiers on both sides noted a period of peace while they collected their food. By 1 December, a British soldier could record a friendly visit from a German sergeant one morning "to see how we were getting on". Relations between French and German units were generally more tense but the same phenomenon began to emerge. In early December, a German surgeon recorded a regular half-hourly truce each evening to recover dead soldiers for burial, during which French and German soldiers exchanged newspapers. This behaviour was often challenged by officers; lieutenant Charles de Gaulle wrote on 7 December of the "lamentable" desire of French infantrymen to leave the enemy in peace, while the commander of 10th Army, Victor d'Urbal, wrote of the "unfortunate consequences" when men "become familiar with their neighbours opposite". Other truces could be forced on both sides by bad weather, especially when trench lines flooded and these often lasted after the weather had cleared.