The War of the Fifth Coalition was a European conflict in 1809 that was part of the Napoleonic Wars and the Coalition Wars. The main conflict took place in Central Europe between the Austrian Empire of Francis I and Napoleon's French Empire. The French were supported by their client states—the Kingdom of Italy, the Confederation of the Rhine and the Duchy of Warsaw. Austria was supported by the Fifth Coalition which included the United Kingdom, Portugal, Spain, and the Kingdoms of Sardinia and Sicily, although the latter two took no part in the fighting. By the start of 1809 much of the French army was committed to the Peninsular War against Britain, Spain and Portugal. After France withdrew 108,000 soldiers from Germany, Austria attacked France to seek the recovery of territories lost in the 1803–1806 War of the Third Coalition. The Austrians hoped Prussia would support them, having recently been defeated by France, but Prussia chose to remain neutral.

On 10 April 1809, Austrian forces under Archduke Charles crossed the border of Bavaria, a French client state. The French response, under Louis-Alexandre Berthier, was disorganised but order was imposed with the arrival of Napoleon on 17 April. Napoleon led an advance to Landshut, hoping to cut off the Austrian line of retreat and sweep into their rear. Charles crossed the Danube at Regensburg, which allowed him to retreat eastwards, although he failed to reach the Austrian capital, Vienna, before the French. A French assault across the Danube was repulsed on 21–22 May at the Battle of Aspern-Essling but a repeat attack was successful in July. Napoleon won a major victory at the 5–6 July Battle of Wagram, which forced the Austrians to sign the Armistice of Znaim on 12 July. Austrian invasions of the Duchy of Warsaw and Saxony (where they fought alongside the Black Brunswickers) were repulsed and they were driven out of their territories in Italy. British forces landed in Walcheren, in the French client state of Holland, but were unable to seize their objective of capturing Antwerp and later withdrew.

The war ended with the Treaty of Schönbrunn, which was regarded as harsh towards Austria as she lost her Mediterranean ports and 20% of her population. Despite the eventual French victory, their defeat at Aspern-Essling showed that Napoleon could be beaten on the battlefield. The war led to the Tyrolean Rebellion, the 1809 Gottscheer rebellion and rebellions in Italy which, although suppressed, foreshadowed future nationalist and anti-French risings. After Schönbrunn, Austria became a French ally, and this was cemented by the marriage of Napoleon to the Austrian princess Marie Louise.

In 1809, Europe was embroiled in warfare, pitting revolutionary France against a series of coalitions in the Coalition Wars almost continuously since 1792. A brief period of peace followed the March 1802 Treaty of Amiens before British-French relations deteriorated, leading to the War of the Third Coalition in May 1803. Britain was joined in their coalition by Sweden in 1804 and Russia and Austria in 1805. In August 1805, the 200,000-strong French Grande Armée invaded the German states, hoping to defeat Austria before Russian forces could intervene. The French emperor Napoleon successfully wheeled his army into the Austrian rear and defeated them at the Battle of Ulm, fought from 15 to 20 October. The Austrian capital, Vienna, was captured in November and a Russo-Austrian army was decisively defeated at the 2 December Battle of Austerlitz. The Treaty of Pressburg, signed soon afterwards, ended Austrian participation in the war.

Austerlitz incited a major shift in the European balance of power. Prussia felt threatened in the region and, alongside Russia, declared war against France in the 1806 War of the Fourth Coalition. After French victories at the Battle of Jena-Auerstadt on 14 October, France occupied the Prussian capital, Berlin. France invaded Poland in November, where Russian forces were stationed, and occupied Warsaw. Russian and French armies fought in February 1807 at the violent, indecisive Battle of Eylau. The action in Poland culminated on 14 June 1807 when the French defeated Russia at the Battle of Friedland. The resulting Treaty of Tilsit in July left France as the dominant power in Western Europe, with many client states including the Duchy of Warsaw. This weakened Prussia and allowed Russia to expand into Finland and South-Eastern Europe.

In 1807, France tried to force Portugal to join the Continental System, a commercial embargo against Britain. When the Portuguese prince regent, John, refused to join, Napoleon sent General Junot to invade Portugal in 1807, resulting in the six year Peninsular War. The war weakened the French empire's military, particularly after Spanish forces and civilians rebelled against France after Napoleon overthrew the Spanish king. After the French defeat at the Battle of Bailén, Napoleon took command of the French forces, defeating the Spanish armies before returning to France. Jean-de-Dieu Soult drove the British out of Spain in the Battle of Corunna in January 1809.

In the beginning of 1809, the French client kingdom of Spain, ruled by Napoleon's brother Joseph Bonaparte, controlled much of Spain and northern Portugal. British and Portuguese forces under Arthur Wellesley launched new offensives from Spring 1809. Spanish regular armies including those led by General Joaquín Blake continued to fight and guerrilla activity in the countryside made French operations hazardous. A significant French presence, numbering 250,000 in June 1809, remained in the peninsula throughout the War of the Fifth Coalition.

The Napoleonic occupation of France's own ally Spain persuaded many in Austria that Napoleon could not be trusted and declaring war was the only way to prevent him from destroying the Habsburg monarchy. The Spanish guerrillas inspired popular resistance against Napoleon, and the Austrians hoped that French preoccupation in Spain would make it easier to defeat France.