The Battle of Austerlitz (2 December 1805/11 Frimaire An XIV FRC), also known as the Battle of the Three Emperors, was one of the most important and decisive engagements of the Napoleonic Wars. The battle occurred near the town of Austerlitz in the Austrian Empire (modern-day Slavkov u Brna in the Czech Republic). Austerlitz brought the War of the Third Coalition to a rapid end, with the Treaty of Pressburg signed by the Austrians later in the month. The battle is often cited as a tactical masterpiece, in the same league as other historic engagements like Cannae or Gaugamela.After eliminating an Austrian army during the Ulm Campaign, French forces seized Vienna in November 1805. The Austrians avoided further conflict until the arrival of the Russians bolstered Allied numbers. Napoleon sent his army north in pursuit of the Allies, but then ordered his forces to retreat so he could feign a grave weakness. Desperate to lure the Allies into battle, Napoleon gave every indication in the days preceding the engagement that the French army was in a pitiful state, even abandoning the dominant Pratzen Heights near Austerlitz. He deployed the French army below the Pratzen Heights and deliberately weakened his right flank, enticing the Allies to launch a major assault there in the hopes of rolling up the whole French line. A forced march from Vienna by Marshal Davout and his III Corps plugged the gap left by Napoleon just in time. Meanwhile, the heavy Allied deployment against the French right weakened the allied center on the Pratzen Heights, which was viciously attacked by the IV Corps of Marshal Soult. With the Allied center demolished, the French swept through both enemy flanks and sent the Allies fleeing chaotically, capturing thousands of prisoners in the process.

The Allied disaster significantly shook the faith of Emperor Francis in the British-led war effort. France and Austria agreed to an armistice immediately and the Treaty of Pressburg followed shortly after, on 26 December. Pressburg took Austria out of both the war and the Coalition while reinforcing the earlier treaties of Campo Formio and of Lunville between the two powers. The treaty confirmed the Austrian loss of lands in Italy and Bavaria to France, and in Germany to Napoleon's German allies. It also imposed an indemnity of 40 million francs on the defeated Habsburgs and allowed the fleeing Russian troops free passage through hostile territories and back to their home soil. Critically, victory at Austerlitz permitted the creation of the Confederation of the Rhine, a collection of German states intended as a buffer zone between France and Central Europe. The Confederation rendered the Holy Roman Empire virtually useless, so the latter collapsed in 1806 after Francis abdicated the imperial throne, keeping Francis I of Austria as his only official title. These achievements, however, did not establish a lasting peace on the continent. Prussian worries about growing French influence in Central Europe sparked the War of the Fourth Coalition in 1806.

The War of the Third Coalition was a European conflict spanning the years 1803 to 1806. During the war, France and its client states under Napoleon I opposed an alliance, the Third Coalition, made up of the United Kingdom, the Holy Roman Empire, the Russian Empire, Naples, Sicily and Sweden. Prussia remained neutral during the war.

Britain had already been at war with France following the breakdown of the Peace of Amiens and remained the only country still at war with France after the Treaty of Pressburg. From 1803 to 1805, Britain stood under constant threat of a French invasion. The Royal Navy, however, secured mastery of the seas and decisively destroyed a Franco-Spanish fleet at the Battle of Trafalgar in October 1805.

The Third Coalition itself came to full fruition in 1804–05 as Napoleon's actions in Italy and Germany (notably the arrest and execution of the Duc d'Enghien) spurred Austria and Russia into joining Britain against France. The war would be determined on the continent, and the major land operations that sealed the swift French victory involved the Ulm Campaign, a large wheeling manoeuvre by the Grande Armée lasting from late August to mid-October 1805 that captured an entire Austrian army, and the decisive French victory over a combined Austro-Russian force under Tsar Alexander I at the Battle of Austerlitz in early December. Austerlitz effectively brought the Third Coalition to an end, although later there was a small side campaign against Naples, which also resulted in a decisive French victory at the Battle of Campo Tenese.

On 26 December 1805, Austria and France signed the Treaty of Pressburg, which took Austria out of both the war and the Coalition, while it reinforced the earlier treaties of Campo Formio and of Lunéville between the two powers. The treaty confirmed the Austrian cession of lands in Italy and Bavaria to France and in Germany to Napoleon's German allies, imposed an indemnity of 40 million francs on the defeated Habsburgs, and allowed the defeated Russian troops free passage, with their arms and equipment, through hostile territories and back to their home soil. Victory at Austerlitz also prompted Napoleon to create the Confederation of the Rhine, a collection of German client states which pledged themselves to raise an army of 63,000 men. As a direct consequence of these events, the Holy Roman Empire ceased to exist when, in 1806, Francis II abdicated the Imperial throne, emerging as Francis I, Emperor of Austria. These achievements, however, did not establish a lasting peace on the continent. Austerlitz had driven neither Russia nor Britain, whose armies protected Sicily from a French invasion, to settle. Meanwhile, Prussian worries about the growing French influence in Central Europe sparked the War of the Fourth Coalition in 1806.