Late on Christmas Eve 1914, men of the British Expeditionary Force (BEF) heard Germans troops in the trenches opposite them singing carols and patriotic songs and saw lanterns and small fir trees along their trenches. Messages began to be shouted between the trenches.
The following day, British and German soldiers met in no man's land and exchanged gifts, took photographs and some played impromptu games of football. They also buried casualties and repaired trenches and dugouts. After Boxing Day, meetings in no man's land dwindled out.
The truce was not observed everywhere along the Western Front. Elsewhere the fighting continued and casualties did occur on Christmas Day. Some officers were unhappy at the truce and worried that it would undermine fighting spirit.
After 1914, the High Commands on both sides tried to prevent any truces on a similar scale happening again. Despite this, there were some isolated incidents of soldiers holding brief truces later in the war, and not only at Christmas.
British Imperial War Museum, The Real Story of the Christmas Truce
"It is rather for us to be here dedicated to the great task remaining before us — that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion — that we here highly resolve that these dead shall not have died in vain, that this nation under God shall have a new birth of freedom, and that government of the people, by the people, for the people shall not perish from the earth.” Abraham Lincoln, November 19, 1863