The Walcheren Campaign was an unsuccessful British expedition to the Netherlands in 1809 intended to open another front in the Austrian Empire's struggle with France during the War of the Fifth Coalition. Sir John Pitt, 2nd Earl of Chatham, was the commander of the expedition, with the missions of capturing Flushing and Antwerp in the Netherlands and enabling navigation of the Scheldt River. Some 39,000 soldiers and 15,000 horses, together with field artillery and two siege trains, crossed the North Sea and landed at Walcheren on 30 July. This was the largest British expedition of that year, larger than the army serving in the Peninsular War in Portugal. Nevertheless, it failed to achieve any of its goals. The Walcheren Campaign involved little fighting, but heavy losses from the sickness popularly dubbed "Walcheren Fever". Although more than 4,000 British troops died during the expedition, only 106 died in combat; the survivors withdrew on 9 December.

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.