The 2004 Madrid train bombings (also known in Spain as 11M) were a series of coordinated, nearly simultaneous bombings against the Cercanas commuter train system of Madrid, Spain, on the morning of 11 March 2004three days before Spain's general elections. The explosions killed 193 people and injured around 2,000. The bombings constituted the deadliest terrorist attack carried out in the history of Spain and the deadliest in Europe since 1988. The official investigation by the Spanish judiciary found that the attacks were directed by Al-Qaeda in Iraq, allegedly as a reaction to Spain's involvement in the 2003 US-led invasion of Iraq. Although they had no role in the planning or implementation, the Spanish miners who sold the explosives to the terrorists were also arrested.Controversy regarding the handling and representation of the bombings by the government arose, with Spain's two main political parties Spanish Socialist Workers' Party (PSOE) and 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 Jos Mara 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.Following the attacks, there were nationwide demonstrations and protests demanding that the government "tell the truth". The prevailing opinion of political analysts is that the Aznar administration lost the general elections as a result of the handling and representation of the terrorist attacks, rather than because of the bombings per se. Results published in The Review of Economics and Statistics by economist Jose G. Montalvo seem to suggest that indeed the bombings had important electoral impact (turning the electoral outcome against the incumbent People's Party and handing government over to the Socialist Party, PSOE).

After 21 months of investigation, judge Juan del Olmo tried Moroccan national Jamal Zougam, among several others, for his participation carrying out the attack. The September 2007 sentence established no known mastermind nor direct al-Qaeda link.

Islamic terrorism (also Islamist terrorism or radical Islamic terrorism) refers to terrorist acts with religious motivations carried out by fundamentalist militant Islamists and Islamic extremists.

Incidents and fatalities from Islamic terrorism have been concentrated in eight Muslim-majority countries (Afghanistan, Egypt, Iraq, Libya, Nigeria, Pakistan, Somalia, and Syria), while four Islamic extremist groups (Islamic State, Boko Haram, the Taliban, and al-Qaeda) were responsible for 74% of all deaths from terrorism in 2015. These groups all have Salafi or other Sunni beliefs. The annual number of fatalities from terrorist attacks grew sharply from 2011 to 2014 when it reached a peak of 33,438, before declining to 13,826 in 2019.Since at least the 1990s, these terrorist incidents have occurred on a global scale, affecting not only Muslim-majority countries in Africa and Asia, but also Russia, Australia, Canada, Israel, India, the United States, China, Philippines, Thailand and countries within Europe. Such attacks have targeted both Muslims and non-Muslims, with one study finding 80% of terrorist victims to be Muslims. In a number of the worst-affected Muslim-majority regions, these terrorists have been met by armed, independent resistance groups, state actors and their proxies, and elsewhere by condemnation by prominent Islamic figures.Justifications given for attacks on civilians by Islamic extremist groups come from extreme interpretations of the Quran, the hadith, and sharia law. These include retribution by armed jihad for the perceived injustices of unbelievers against Muslims; the belief that the killing of many self-proclaimed Muslims is required because they have violated Islamic law and are disbelievers (takfir); the overriding necessity of restoring and purifying Islam by establishing sharia law, especially by restoring the Caliphate as a pan-Islamic state (especially ISIS); the glory and heavenly rewards of martyrdom; the supremacy of Islam over all other religions.The use of the phrase "Islamic terrorism" is disputed. In Western political speech, it has variously been called "counter-productive", "highly politicized, intellectually contestable" and "damaging to community relations", by those who disapprove of the characterization 'Islamic'.

Others have condemned the avoidance of the term as an act of "self-deception", "full-blown censorship" and "intellectual dishonesty".