The Battle of Lyndanisse (also spelled the Battle of Lindanise) was a battle during the Livonian Crusade, fought by the Kingdom of Denmark and German allies against pagan Estonian tribes. The battle helped King Valdemar II of Denmark establish the territory of Danish Estonia during the Northern Crusades, which were undertaken in response to calls from the Pope. The Danes defeated the Estonians at Lindanise (Danish: Lyndanisse, at the site of the later city of Reval, now known as Tallinn).Today, the Battle of Lyndanisse is perhaps best known for a legend that the Danish flag, the Dannebrog, fell from the sky just as the Danes were about to lose the battle.

The Northern Crusades or Baltic Crusades were Christian colonization and Christianization campaigns undertaken by Catholic Christian military orders and kingdoms, primarily against the pagan Baltic, Finnic and West Slavic peoples around the southern and eastern shores of the Baltic Sea, and to a lesser extent also against Orthodox Christian Slavs (East Slavs).

The most notable campaigns were the Livonian and Prussian crusades. Some of these wars were called crusades during the Middle Ages, but others, including most of the Swedish ones, were first dubbed crusades by 19th-century romantic nationalist historians. However, crusades against Estonians, but also against 'other pagans in those parts' were authorized by Pope Alexander III in the bull Non parum animus noster, in 1171 or 1172.