The Gunpowder Plot of 1605, in earlier centuries often called the Gunpowder Treason Plot or the Jesuit Treason, was a failed assassination attempt against King James I by a group of provincial English Catholics led by Robert Catesby who sought to restore the Catholic monarchy to England after decades of persecution against Catholics.

The plan was to blow up the House of Lords during the State Opening of Parliament on 5 November 1605, as the prelude to a popular revolt in the Midlands during which James's nine-year-old daughter, Elizabeth, was to be installed as the Catholic head of state. Catesby may have embarked on the scheme after hopes of securing greater religious tolerance under King James had faded, leaving many English Catholics disappointed. His fellow traitors were John and Christopher Wright, Robert and Thomas Wintour, Thomas Percy, Guy Fawkes, Robert Keyes, Thomas Bates, John Grant, Ambrose Rookwood, Sir Everard Digby and Francis Tresham. Fawkes, who had 10 years of military experience fighting in the Spanish Netherlands in the failed suppression of the Dutch Revolt, was given charge of the explosives.

The plot was revealed to the authorities in an anonymous letter sent to William Parker, 4th Baron Monteagle, on 26 October 1605. During a search of the House of Lords in the evening on 4 November 1605, Fawkes was discovered guarding 36 barrels of gunpowder—enough to reduce the House of Lords to rubble—and arrested. Most of the conspirators fled from London as they learned that the plot had been discovered, trying to enlist support along the way. Several made a stand against the pursuing Sheriff of Worcester and his men at Holbeche House; in the ensuing battle Catesby was one of those shot and killed. At their trial on 27 January 1606 eight of the survivors, including Fawkes, were convicted and sentenced to be hanged, drawn and quartered.

Details of the assassination attempt were allegedly known by the principal Jesuit of England, Father Henry Garnet. Although he was convicted of treason and sentenced to death, doubt has been cast on how much he really knew of the plot. As its existence was revealed to him through confession, Garnet was prevented from informing the authorities by the absolute confidentiality of the confessional. Although anti-Catholic legislation was introduced soon after the discovery of the plot, many important and loyal Catholics retained high office during King James I's reign. The thwarting of the Gunpowder Plot was commemorated for many years afterwards by special sermons and other public events such as the ringing of church bells, which evolved into the British variant of Bonfire Night of today.