Terrorism in Europe has a long and bloody history. This has often been linked to nationalist and separatist movements (separating countries), while other acts have been related to politics (including anarchism, far-right and far-left extremism), religious extremism, or organized crime. Terrorism in the European sections of the Eurasian countries of Turkey and Russia are not included in this list.

There are more than one hundred definitions of terrorism in scholarly literature. Because the term is used in polemical contexts, the word itself can become part of the campaign. A simple definition would be "use of force against innocent people for political purposes". Some scholars argue that there is no true or correct definition due to terrorism being an abstract concept without a real presence. Legal definitions contain internal contradictions and might be misused. There is an overlap between terrorism and various other forms of conflict and violent action, including civil wars or non-international armed conflicts. This is the case with several significant non-international conflicts in Europe, where there thus can be dispute as to what counts as terrorism: examples include the Irish War of Independence (1919–21), the breakup of Yugoslavia and subsequent conflicts, the First (1994–6) and Second Chechen Wars (1999–2009), and the War of Dagestan (1999).

In the Middle Ages, maritime nations in Europe sponsored pirates and privateering against rivals, which can be compared to terrorism. The term "terror" is used about the reign of terror in France, carried out by the Jacobins in 1792-4.

Terrorism in Europe around the beginning of the twentieth century was often associated with anarchism.

Terrorism within the European Communities since 1951 has often been linked to separatist movements, including the Irish Republican Army within the United Kingdom, and Euskadi Ta Askatasuna within Spain. Other perpetrators have been linked to far-right and far-left extremism, environmental extremism and anarchism. Since 2001, there has been an increase in attacks linked to extremist groups, particularly in France. Many separatist terrorist activities also have a religious angle, as, for example, with Chechen separatism in Russia.^{[citation needed]}

There have been recent increases in the number of high-fatality attacks. There had been a decrease in the number of overall fatalities from terrorist attacks between 1990 and 2015, compared to those between 1970 and 1990. Prior to 1990, on average 150 people died each year from terrorist attacks; this figure would be even higher if the large number of people who died in 1988 from the Pan Am 2013 bombing were included. From 1990, an average of a little under 50 people died each year. There was an increase of fatalities from 2011, with the attacks by far-right extremist Anders Breivik in Norway, and Islamist extremist attacks in France in 2015 and 2016.

Europol has published an annual trend report on terrorist attacks (including failed, foiled, and completed attacks) and terrorist-related arrests in the EU since 2006. The reports identify that perpetrators' known or suspected affiliations have been disparate in nature. Europol break these down into five categories: jihadist terrorism (previously termed "religiously-inspired terrorism"); ethno-nationalist and separatist terrorism; left-wing and anarchist terrorism; right-wing terrorism; and single-issue terrorism. Europol's reports do not provide a breakdown of the proportion of attacks that have been completed or the type of damage inflicted. According to these data, the vast majority of terrorist attacks in the EU between 2006 and 2013 were affiliated with ethnonational or separatist motives, followed by left-wing and anarchist attacks, and those that are registered as 'unspecified'. A significant number of terror attacks were motivated religiously or associated with right-wing groups. Among those arrested on terror-related crimes, most were religiously motivated and form the largest group, followed by separatist related terror suspects.

In 2015, a total of 211 completed, failed, or foiled terrorist attacks were reported by EU states, resulting in 151 fatalities (of which 148 were in France, with 130 of them occurring during the November 2015 Paris attacks) and over 360 people injured. As in previous years, separatist attacks accounted for the largest proportion (65), followed by jihadist attacks (17). Jihadist attacks caused the largest number of fatalities (150) and injuries (250). The United Kingdom reported the largest number of attacks (103) but did not provide statistics on suspected affiliation. Tackling jihadist terrorism threats has become an over-riding priority for security services, although many commentators express concerns that the risk of far-right terrorism is currently being underestimated.