The Battle of Eylau, or Battle of Preussisch-Eylau, was a bloody and strategically inconclusive battle on 7 and 8 February 1807 between Napoleon's Grande Armée and the Imperial Russian Army under the command of Levin August von Bennigsen near the town of Preussisch Eylau in East Prussia. Late in the battle, the Russians received timely reinforcements from a Prussian division of von L'Estocq. After 1945, the town was renamed Bagrationovsk as part of Kaliningrad Oblast, Russia. The engagement was fought during the War of the Fourth Coalition, part of the Napoleonic Wars.

La Grande Armée was the main military component of the French Imperial Army commanded by Emperor Napoleon Bonaparte during the Napoleonic Wars. From 1804 to 1808, it won a series of military victories that allowed the French Empire to exercise unprecedented control over most of Europe. Widely acknowledged to be one of the greatest fighting forces ever assembled, it suffered enormous losses during the disastrous Peninsular War followed by the invasion of Russia in 1812, after which it never recovered its strategic superiority and ended in total defeat for Napoleonic France by the Peace of Paris in 1815.