The Battle of Blenheim (German: Zweite Schlacht bei Hchstdt; French: Bataille de Hchstdt; Dutch: Slag bij Blenheim) fought on 13 August [O.S. 2 August] 1704, was a major battle of the War of the Spanish Succession. The overwhelming Allied victory ensured the safety of Vienna from the Franco-Bavarian army, thus preventing the collapse of the reconstituted Grand Alliance.

Louis XIV of France sought to knock the Holy Roman Emperor, Leopold, out of the war by seizing Vienna, the Habsburg capital, and gain a favourable peace settlement. The dangers to Vienna were considerable: Maximilian II Emanuel, Elector of Bavaria, and Marshal Ferdinand de Marsin's forces in Bavaria threatened from the west, and Marshal Louis Joseph de Bourbon, duc de Vendme's large army in northern Italy posed a serious danger with a potential offensive through the Brenner Pass. Vienna was also under pressure from Rkczi's Hungarian revolt from its eastern approaches. Realising the danger, the Duke of Marlborough resolved to alleviate the peril to Vienna by marching his forces south from Bedburg to help maintain Emperor Leopold within the Grand Alliance.

A combination of deception and skilled administration designed to conceal his true destination from friend and foe alike enabled Marlborough to march 400 km (250 mi) unhindered from the Low Countries to the River Danube in five weeks. After securing Donauwrth on the Danube, Marlborough sought to engage Maximilian's and Marsin's army before Marshal Camille d'Hostun, duc de Tallard, could bring reinforcements through the Black Forest. The Franco-Bavarian commanders proved reluctant to fight until their numbers were deemed sufficient, and Marlborough failed in his attempts to force an engagement. When Tallard arrived to bolster Maximilian's army, and Prince Eugene of Savoy arrived with reinforcements for the Allies, the two armies finally met on the banks of the Danube in and around the small village of Blindheim, from which the English "Blenheim" is derived.

Blenheim was one of the battles that altered the course of the war, which until then was favouring the French and Spanish Bourbons. Although the battle did not win the war, it prevented a potentially devastating loss for the Grand Alliance and shifted the war's momentum, ending French plans of knocking Emperor Leopold out of the war. The French suffered catastrophic casualties in the battle including their commander-in-chief, Tallard, who was taken captive to England. Before the 1704 campaign ended, the Allies had taken Landau, and the towns of Trier and Trarbach on the Moselle in preparation for the following year's campaign into France itself. This offensive never materialised as the Grand Alliance's army had to depart the Moselle to defend Lige from a French counter-offensive. The war raged on for another decade before ending in 1714.

The War of the Spanish Succession (1701–1715) was a conflict involving many of the leading European powers that was triggered by the death in November 1700 of the childless Charles II of Spain. It established the principle that dynastic rights were secondary to maintaining the balance of power between different countries. Related conflicts include the 1700–1721 Great Northern War, Rákóczi's War of Independence in Hungary, the Camisards revolt in southern France, Queen Anne's War in North America and minor struggles in colonial India.

Although weakened by over a century of continuous conflict, in 1700 the Spanish Empire remained a global power with its vast dominions including the Spanish Netherlands, large parts of Italy, the Philippines, and much of the Americas. Charles's closest heirs were members of the Austrian Habsburgs or French Bourbons; acquisition of an undivided Spanish Empire by either threatened the European balance of power.

Attempts by Louis XIV of France and William III of England to partition the empire in 1698 and 1700 were rejected by the Spanish. Instead, Charles named Philip of Anjou, a grandson of Louis XIV, as his heir; if he refused, the alternative was Archduke Charles, younger son of Leopold I, Holy Roman Emperor. Having accepted, Philip was proclaimed king of an undivided Spanish Empire on 16 November 1700. The proclamation led to war, with France and Spain on one side and the Grand Alliance on the other to maintain the separation of the Spanish and French thrones.

The French held the advantage in the early stages, but were forced onto the defensive after 1706; however, by 1710 the Allies had failed to make any significant progress, while Bourbon victories in Spain had secured Philip's position as king. When Emperor Joseph I died in 1711, Archduke Charles succeeded his brother as emperor, and the new British government initiated peace talks. Since only British subsidies kept their allies in the war, this resulted in the 1713–15 Peace of Utrecht treaties, followed by the 1714 Treaties of Rastatt and Baden.

Philip was confirmed as king of Spain in return for renouncing the right of himself or his descendants to inherit the French throne; the Spanish Empire remained largely intact, but ceded territories in Italy and the Low Countries to Austria and Savoy. Britain retained Gibraltar and Menorca which it captured during the war, acquired significant trade concessions in the Spanish Americas, and replaced the Dutch as the leading maritime and commercial European power. The Dutch gained a strengthened defence line in what was now the Austrian Netherlands; although they remained a major commercial power, the cost of the war permanently damaged their economy.

France withdrew backing for the exiled Jacobites and recognised the Hanoverians as heirs to the British throne; ensuring a friendly Spain was a major achievement, but left them financially exhausted. The decentralisation of the Holy Roman Empire continued, with Prussia, Bavaria and Saxony increasingly acting as independent states. Combined with victories over the Ottomans, this meant the Austrian Habsburgs increasingly switched their focus to southern Europe.