The Grande Armée (pronounced [ɡʁɑ̃d aʁme]; French for 'Great Army') was the primary field army of the French Imperial Army during the Napoleonic Wars. Commanded by Napoleon, from 1804 to 1808 it won a series of military victories that allowed the First French Empire to exercise unprecedented control over most of Europe. Widely acknowledged to be one of the greatest fighting forces ever assembled, it suffered catastrophic losses during the disastrous French invasion of Russia, after which it never recovered its strategic superiority and ended its military career with a total defeat during the Hundred Days in 1815.

The Grande Armée was formed in 1804 from the Army of the Coasts of the Ocean, a field army of over 100,000 men assembled for Napoleon's planned invasion of the United Kingdom. He subsequently led the field army to Central Europe and defeated Austrian and Russian forces as part of the War of the Third Coalition. Thereafter, the Grande Armée was the principal field army deployed in the War of the Fourth Coalition, Peninsular War and War of the Fifth Coalition, where the French army slowly lost a large portion of its veteran soldiers, strength and prestige, and in the invasion of Russia, War of the Sixth Coalition and Hundred Days. The term Grande Armée is often used to refer to multinational armies led by Napoleon in his campaigns.

In addition to its size and multinational composition, the Grande Armée was known for its innovative formations, tactics, logistics and communications. While most contingents were commanded by French generals, except for the Polish and Austrian contingent, soldiers could climb the ranks regardless of class, wealth, or national origin, unlike many other European armies of the era. Upon its formation, the Grande Armée consisted of six corps led by Napoleon's marshals and senior generals. When the Austrian and Russian armies began their preparations to invade France in late 1805, the Grande Armée was quickly ordered across the Rhine into southern Germany, leading to Napoleon's victories at Ulm and Austerlitz. The French army grew as Napoleon seized power across Europe, recruiting troops from occupied and allied nations; it reached its peak of one million men at the start of the Russian campaign in 1812, with the Grande Armée reaching its height of 413,000 French soldiers and over 600,000 men overall when including foreign recruits.

In summer of 1812, as large of an amount as 300,000 French troops fought in the Peninsular War (see fr:Armée d'Espagne). Napoleon opened a second war front as the Grande Armée marched slowly east, and the Russians fell back with its approach. After the capture of Smolensk and tactical victory at Borodino, the French reached Moscow on 14 September 1812. However, the army was already drastically reduced by skirmishes with the Russians, disease (principally typhus), desertion, heat, exhaustion, and long communication lines. The army spent a month in Moscow but was ultimately forced to march back westward. Cold, starvation, and disease, as well as constant harassment by Cossacks and Russian partisans, resulted in the Grande Armée's utter destruction as a fighting force. Only 120,000 men survived to leave Russia (excluding early deserters); of these, 50,000 were Austrians, Prussians, and other Germans, 20,000 were Poles, and just 35,000 were French. As many as 380,000 died in the campaign. Napoleon led a new army during the campaign in Germany in 1813, the defense of France in 1814, and the Waterloo campaign in 1815, but the Grande Armée would never regain its height of June 1812, and France would find itself invaded on multiple fronts from the Spanish border to the German border. In total, from 1805 to 1813, over 2.1 million Frenchmen were conscripted into the French Imperial Army.

For a history of the French Army in the period of 1792–1804 during the wars of the First and Second Coalitions see French Revolutionary Army.

The Grande Armée was originally formed as L'Armée des côtes de l'Océan (Army of the Ocean Coasts) intended for the invasion of Britain, at the port of Boulogne in 1804. Following Napoleon's coronation as Emperor of the French in 1804, the Third Coalition was formed against France and the Grande Armée turned its sights eastwards in 1805. The army left Boulogne in late August and through rapid marches, surrounded General Karl von Mack's isolated Austrian Army at the fortress of Ulm. The Ulm campaign, as it came to be known, resulted in 60,000 Austrian prisoners at the cost of just 2,000 French soldiers. By November, Vienna was taken but Austria refused to capitulate, maintaining an army in the field. In addition, its ally Russia had yet to commit to action. The war would continue for a while longer. Affairs were decisively settled on 2 December 1805 at the Battle of Austerlitz, where the numerically inferior Grande Armée routed a combined Russo-Austrian army led by Russian Emperor Alexander I. The stunning victory led to the Treaty of Pressburg on 26 December 1805, with the dissolution of the Holy Roman Empire the following year.

The alarming increase of French power in Central Europe disturbed Prussia, which had remained neutral the previous year. After much diplomatic wrangling, Prussia secured promises of Russian military aid and the Fourth Coalition against France came into being in 1806. The Grande Armée advanced into Prussian territory with the famed bataillon-carré (battalion square) system, whereby corps marched in close supporting distances and became vanguards, rearguards, or flank forces as the situation demanded, and decisively defeated the Prussians at Jena and Auerstedt, both fought on 14 October 1806. After a legendary pursuit, the French took 140,000 prisoners and killed and wounded roughly 25,000. Marshal Louis-Nicolas Davout's III Corps, the victors at Auerstedt, received the honours of marching into Berlin first. Once more, the French had defeated an enemy before its allies could arrive, and once more, this did not bring peace.

Napoleon now turned his attentions to Poland, where the remaining Prussian armies were linking up with their Russian allies. A difficult winter campaign produced nothing but a stalemate, made worse by the Battle of Eylau on 7–8 February 1807, where Russian and French casualties soared for little gain. The campaign resumed in the spring and this time General Levin August von Bennigsen's Russian army was soundly defeated at the Battle of Friedland on 14 June 1807. This victory brought about the Treaties of Tilsit between France, Russia, and Prussia in July, leaving Napoleon with no enemies on the continent.