The Battle of Trafalgar (21 October 1805) was a naval engagement fought by the British Royal Navy against the combined fleets of the French Navy and Spanish Navy, during the War of the Third Coalition (August–December 1805) of the Napoleonic Wars (1803–1815).

The battle was the most decisive British naval victory of the war. Twenty-seven British ships of the line led by Admiral Lord Nelson aboard HMS Victory defeated thirty-three French and Spanish ships of the line under French Admiral Pierre-Charles Villeneuve off the south-west coast of Spain, just west of Cape Trafalgar. The Franco-Spanish fleet lost twenty-two ships, without a single British vessel being lost.

The British victory spectacularly confirmed the naval supremacy that Britain had established during the previous century and was achieved in part through Nelson's departure from the prevailing naval tactical orthodoxy, which involved engaging an enemy fleet in a single line of battle parallel to the enemy to facilitate signalling in battle and disengagement, and to maximise fields of fire and target areas. Nelson instead divided his smaller force into two columns directed perpendicularly against the larger enemy fleet, with decisive results.