The 2004 Madrid train bombings (also known in Spain as 11M for 11 de marzo) were a series of coordinated, nearly simultaneous bombings against the Cercanías commuter train system of Madrid, Spain, on the morning of 11 March 2004—three days before Spain's general elections. The explosions killed 193 people and injured around 2,500. The bombings constituted the deadliest terrorist attack carried out in the history of Spain and the deadliest in Europe since the bombing of Pan Am Flight 103 in 1988 in Scotland. The attacks were carried out by radical Islamists who opposed Spanish indirect involvement in the 2003 US-led invasion of Iraq.
Controversy regarding the handling and representation of the bombings by the government arose, with Spain's two main political parties—the Spanish Socialist Workers' Party (PSOE) and the Partido Popular (PP)—accusing each other of concealing or distorting evidence for electoral reasons. The bombings occurred three days before general elections in which incumbent Prime Minister José María Aznar's PP was defeated. Immediately after the bombing, leaders of the PP claimed evidence indicating the Basque separatist organization ETA (Euskadi Ta Askatasuna) was responsible for the bombings, while the opposition claimed that the PP was trying to prevent the public from knowing it had been an Islamist attack, which would be interpreted as the direct result of Spain's involvement in Iraq, an unpopular war which the government had entered without the approval of the Spanish Parliament. The scale and precise planning of the attacks reared memories of the September 11 attacks.