The Battle of Nrdlingen (German: Schlacht bei Nrdlingen; Spanish: Batalla de Nrdlingen; Swedish: Slaget vid Nrdlingen) took place on 6 September 1634 during the Thirty Years' War. A combined Imperial-Spanish force won a crushing victory over a Swedish-German army.

By 1634, the Swedes and their Protestant German allies occupied much of southern Germany and blocked the Spanish Road, an overland supply route used by the Spanish to funnel troops and supplies from Italy to support their ongoing war against the Dutch Republic. In order to regain control of this, a Spanish army under Cardinal-Infante Ferdinand linked up with an Imperial force led by Ferdinand of Hungary near the town of Nrdlingen, which was held by a Swedish garrison.

A Swedish-German army commanded by Gustav Horn and Bernhard of Saxe-Weimar marched to its relief but they significantly underestimated the number and calibre of the Imperial-Spanish troops facing them. On 6 September, Horn launched a series of assaults against earthworks constructed on the hills to the south of Nrdlingen, all of which were repulsed. Superior numbers meant the Spanish-Imperial commanders could continually reinforce their positions and Horn eventually began to retreat. As they did so, they were outflanked by Imperial cavalry and the Protestant army collapsed.

Defeat had far-reaching territorial and strategic consequences; the Swedes withdrew from Bavaria and under the terms of the Peace of Prague in May 1635, their German allies made peace with Emperor Ferdinand II. France, which had previously restricted itself to funding the Swedes and Dutch, formally became an ally and entered the war as an active belligerent.

The Thirty Years' War was a conflict fought largely within the Holy Roman Empire from 1618 to 1648. Considered one of the most destructive wars in European history, estimates of total deaths caused by the conflict range from 4.5 to 8 million, while some areas of Germany experienced population declines of over 50%. Related conflicts include the Eighty Years' War, the War of the Mantuan Succession, the Franco-Spanish War, and the Portuguese Restoration War.

Until the 20th century, historians considered it a continuation of the German religious struggle initiated by the Reformation and ended by the 1555 Peace of Augsburg. This divided the Empire into Lutheran and Catholic states, but over the next 50 years the expansion of Protestantism beyond these boundaries gradually destabilised Imperial authority. While religion was a significant factor in starting the war, scholars generally agree that its scope and extent was driven by the contest for European dominance between Habsburgs in Austria and Spain, and the French House of Bourbon.The war began in 1618 when Ferdinand II was deposed as King of Bohemia and replaced by Frederick V of the Palatinate. Although the Bohemian Revolt was quickly suppressed, fighting expanded into the Palatinate, whose strategic importance drew in the Dutch Republic and Spain, then engaged in the Eighty Years War. Since ambitious external rulers like Christian IV of Denmark and Gustavus Adolphus of Sweden also held territories within the Empire, what began as an internal dynastic dispute was transformed into a far more destructive European conflict.

The first phase from 1618 until 1635 was primarily a civil war between German members of the Holy Roman Empire, with external powers playing supportive roles. After 1635, the Empire became one theatre in a wider struggle between France, supported by Sweden, and Spain in alliance with Emperor Ferdinand III. This concluded with the 1648 Peace of Westphalia, whose provisions included greater autonomy within the Empire for states like Bavaria and Saxony, as well as acceptance of Dutch independence by Spain. By weakening the Habsburgs relative to France, the conflict altered the European balance of power and set the stage for the wars of Louis XIV.