The deadly attacks on Tuesday at Brussels Airport and a metro station in the Belgian capital are the latest to hit Europe.
Here is an overview of other major ones:
November 13, 2015: Armed men linked to the Islamic State of Iraq and the Levant (ISIL also known as ISIS) group attack the Bataclan concert hall and other sites across Paris, killing 130 people. A key suspect in the attack, 26-year-old Salah Abdeslam was arrested in Brussels on March 18, 2016.
February 14, 2015: A gunman kills Danish filmmaker Finn Norgaard and wounds three police officers in Copenhagen. A day later the gunman, Omar El-Hussein, attacks a synagogue, killing a Jewish guard and wounding two police officers before being shot dead.
January 7, 2015: A gun assault on the Paris offices of the satirical magazine Charlie Hebdo kills 12 people. Al-Qaeda in the Arabian Peninsula claims responsibility for the attack, saying it was in revenge for Charlie Hebdo's depictions of the Prophet Muhammad.
May 24, 2014: Four people are killed at the Jewish Museum in Brussels by an intruder with a Kalashnikov. The accused is a former French fighter linked to ISIL.
May 22, 2013: Two suspected al-Qaeda-inspired gunmen run down British soldier Lee Rigby in a London street, then stab and hack him to death.
March 2012: French gunman Mohammed Merah, claiming links to al-Qaeda, kills three Jewish schoolchildren, a rabbi and three paratroopers in Toulouse, southern France.
July 22, 2011: Anti-Muslim Anders Behring Breivik plants a bomb in Oslo then launches a shooting massacre on a youth camp on Norway's Utoya island, killing 77 people, many of them teenagers.
November 2, 2011: The offices of Charlie Hebdo in Paris are firebombed after the satirical magazine runs a cover featuring a caricature of the Prophet Muhammad. No one is injured.
March 2, 2011: An armed gunman Arid Uka shoots dead two US airmen and injures two others at Frankfurt airport, after apparently being inspired by a fake internet video purporting to show American atrocities in Afghanistan.
July 7, 2005: 52 commuters are killed in London when four al-Qaeda-inspired suicide bombers blow themselves up on three subway trains and a bus.
March 11, 2004: Bombs on four Madrid commuter trains in the morning rush hour kill 191 people in Europe's worst attack.