The Eighty Years' War or Dutch Revolt (Dutch: Tachtigjaarige Oorlog or Nederlandse Opstand; c. 1566/1568–1648) was an armed conflict in the Habsburg Netherlands between disparate groups of rebels and the Spanish government. The causes of the war included the Reformation, centralisation, excessive taxation, and the rights and privileges of the Dutch nobility and cities.

After the initial stages, Philip II of Spain, the sovereign of the Netherlands, deployed his armies and regained control over most of the rebel-held territories. However, widespread mutinies in the Spanish army caused a general uprising. Under the leadership of the exiled William the Silent, the Catholic and Protestant-dominated provinces sought to establish religious peace while jointly opposing the king's regime with the Pacification of Ghent, but the general rebellion failed to sustain itself.

Despite steady military and diplomatic successes by the Governor of Spanish Netherlands and General for Spain, the Duke of Parma, the Union of Utrecht continued their resistance, proclaiming their independence through the 1581 Act of Abjuration and establishing the Calvinist-dominated Dutch Republic in 1588. In the Ten Years thereafter, the Republic (whose heartland was no longer threatened) made conquests in the north and east and received diplomatic recognition from France and England in 1596. The Dutch colonial empire emerged, which began with Dutch attacks on Portugal's overseas territories.

Facing a stalemate, the two sides agreed to a Twelve Years' Truce in 1609; when it expired in 1621, fighting resumed as part of the broader Thirty Years' War. An end was reached in 1648 with the Peace of Münster when Spain retained the Southern Netherlands and recognised the Dutch Republic as an independent country.

The origins of the Eighty Years' War are complicated, and have been a source of disputes amongst historians for centuries.

The Habsburg Netherlands emerged as a result of the territorial expansion of the Burgundian State in the 14th and 15th centuries. Upon extinction of the Burgundian State in 1477/1482, these lands were inherited by the House of Habsburg, whose Charles V became both King of Spain and Holy Roman Emperor. By conquering the rest of what would become the "Seventeen Provinces" during the Guelders Wars (1502–1543), and seeking to combine these disparate regions into a single political entity, Charles aspired to counter the Protestant Reformation and keep all his subjects obedient to the Catholic Church.

The period between the start of the Beeldenstorm in August 1566 until early 1572 (before the Capture of Brielle on 1 April 1572) contained the first events of a series that would later be known as the Eighty Years' War between the Spanish Empire and disparate groups of rebels in the Habsburg Netherlands. Some of the first pitched battles and sieges between radical Calvinists and Habsburg governmental forces took place in the years 1566–1567, followed by the arrival and government takeover by Fernando Álvarez de Toledo, 3rd Duke of Alba (simply known as "Alba" or "Alva") with an army of 10,000 Spanish and Italian soldiers. Next, an ill-fated invasion by the most powerful nobleman of the Low Countries, the exiled but still-Catholic William "the Silent" of Orange, failed to inspire a general anti-government revolt. Although the war seemed over before it got underway, in the years 1569–1571, Alba's repression grew severe, and opposition against his regime mounted to new heights and became susceptible to rebellion.

The period between the Capture of Brielle (1 April 1572) and the Pacification of Ghent (8 November 1576) was an early stage of the Eighty Years' War (c. 1568–1648) between the Spanish Empire and groups of rebels in the Habsburg Netherlands.