The Ulm campaign was a series of French and Bavarian military maneuvers and battles to outflank and capture an Austrian army in 1805 during the War of the Third Coalition. It took place in the vicinity of and inside the Swabian city of Ulm. The French Grande Armée, led by Emperor Napoleon, had 210,000 troops organized into seven corps and hoped to knock out the Austrian army in the Danube before Russian reinforcements could arrive. Rapid marching let Napoleon conduct a large wheeling maneuver, which captured an Austrian army of 60,000 under Feldmarschall-Leutnant (FML) Karl Freiherr Mack von Leiberich on 20 October at Ulm. The campaign is by some military historians regarded as a strategic masterpiece and was influential in the development of the Schlieffen Plan in the late 19th century. Napoleon himself wrote:

The victory at Ulm did not end the war since a large Russian army under Mikhail Kutuzov was near Vienna to defend the city against the French. The Russians withdrew to the northeast to await reinforcements and to link up with Austrian army units. The French moved aggressively forward and captured Vienna on 12 November. On 2 December, the massive Battle of Austerlitz, causing 24,000 to 36,000 casualties, removed Austria from the war. The resulting Treaty of Pressburg in late December brought the Third Coalition to an end and established Napoleonic France as the major power in Central Europe, which led to the War of the Fourth Coalition against the Kingdom of Prussia and Russia the following year.

Europe had been by then embroiled in the French Revolutionary Wars since 1792. After five years of war, the French Republic subdued the First Coalition in 1797. A Second Coalition was formed in 1798 but this too was defeated by 1801. Britain remained the only opponent for the new French Consulate. In March 1802, France and Britain agreed to end hostilities under the Treaty of Amiens. For the first time in ten years, all of Europe was at peace. There were many problems between the two sides and implementing the agreements that had been reached at Amiens seemed to be a growing challenge. Leading British officials resented having to return colonies captured from the French and Dutch, while Napoleon was angered that Britain refused to evacuate Malta as stipulated in the treaty. The tense situation only worsened since Napoleon sent an expeditionary force to retake control of Saint-Domingue from Toussaint Louverture. In May 1803, Britain declared war on France.

In December 1804, an Anglo-Swedish agreement led to the creation of the Third Coalition. British Prime Minister William Pitt the Younger spent 1804 and 1805 in a flurry of diplomatic activity to form a new coalition against France. Mutual suspicion between the British and the Russians eased in the face of several French political mistakes, and by April 1805, the first two had signed a treaty of alliance. Having been defeated twice in recent memory by France and keen on revenge, Austria also joined the coalition a few months later.

Prior to the formation of the Third Coalition, Napoleon had assembled the Army of England, an invasion force meant to carry out planned invasion of Britain, around six camps at Boulogne in Northern France. Although they never set foot on British soil, Napoleon's troops received careful training for any possible military operation. Although boredom quickly set in among the troops, Napoleon paid many visits to conduct lavish parades to maintain their morale.

The units at Boulogne formed the core for what Napoleon would later call "La Grande Armée" ("The Great Army"). At the start, the French army had about 200,000 men organized into seven corps, which were large field units, containing about 36 to 40 cannon each and capable of independent action until other corps could arrive. On top, Napoleon created a cavalry reserve of 22,000 troopers organized into two cuirassier divisions, four mounted dragoon divisions and two divisions of dismounted dragoons and light cavalry, all supported by 24 artillery pieces. By 1805, the Grande Armée had grown to a force of 350,000, was equipped and trained. It possessed a competent officer class where almost all from sergeants to marshals had experience in the recent Revolutionary Wars.

Archduke Charles, brother of the Austrian Emperor, had started to reform the Austrian army in 1801 by taking away power from the Hofkriegsrat (Aulic Council), the military-political council responsible for decision making in the Austrian armed forces. Charles was Austria's most able field commander, but he was unpopular with the royal court and lost much influence when, against his advice, Austria decided to go to war with France.

Mack became the new main commander in Austria's army, instituting reforms on the infantry on the eve of war that called for a regiment to be composed of four battalions of four companies, rather than the older three battalions of six companies. The sudden change came with no corresponding officer training; new units were led by commanders who had not been given sufficient tactical training in using their units.