There are many different categories of terrorism and terrorist groups that are currently in use. These categories serve to differentiate terrorist organizations according to specific criteria, which are usually related to the field or specialty of whoever is selecting the categories. Also, some categories are simply labels appended arbitrarily or redundantly, often by the media. For example, every terrorist organization is by definition "radical", as terror tactics are not the norm for the mainstream of any group.

Separatist. Separatist groups are those with the goal of separation from existing entities through independence, political autonomy, or religious freedom or domination. The ideologies separatists subscribe to include social justice or equity, anti-imperialism, as well as the resistance to conquest or occupation by a foreign power.

Ethnocentric. Groups of this persuasion see race as the defining characteristic of a society, and therefore a basis of cohesion. There is usually the attitude that a particular group is superior because of their inherent racial characteristics.

Nationalistic. The loyalty and devotion to a nation, and the national consciousness derived from placing one nation's culture and interests above those of other nations or groups. This can find expression in the creation of a new nation, or in splitting away part of an existing state to join with another that shares the perceived "national" identity.

Revolutionary. Dedicated to the overthrow of an established order and replacing it with a new political or social structure. Although often associated with communist political ideologies, this is not always the case, and other political movements can advocate revolutionary methods to achieve their goals.

Political. Political ideologies are concerned with the structure and organization of the forms of government and communities. While observers outside terrorist organizations may stress differences in political ideology, the activities of groups that are diametrically opposed on the political spectrum are similar to each other in practice.

Religious. Religiously inspired terrorism is on the rise, with a forty-three percent increase of total international terror groups espousing religious motivation between 1980 and 1995. While Islamic terrorists and organizations have been the most active, and the greatest recent threat to the United States, all of the major world religions have extremists that have taken up violence to further their perceived religious goals. Religiously motivated terrorists see their objectives as holy writ, and therefore infallible and non-negotiable

Social. Often particular social policies or issues will be so contentious that they will incite extremist behavior and terrorism. Frequently this is referred to as "single issue" or "special interest" terrorism. Some issues that have produced terrorist activities in the United States and other countries include animal rights, abortion, ecology/environment, and minority rights.

Domestic. These terrorists are "home-grown" and operate within and against their home country. They are frequently tied to extreme social or political factions within a particular society, and focus their efforts specifically on their nation's socio-political arena.

International or Transnational. Often describing the support and operational reach of a group, these terms are often loosely defined, and can be applied to widely different capabilities. International groups typically operate in multiple countries, but retain a geographic focus for their activities. Hezbollah has cells worldwide, and has conducted operations in multiple countries, but is primarily concerned with events in Lebanon and Israel.

Transnational groups operate internationally, but are not tied to a particular country, or even region. Al Qaeda is transnational; being made up of many nationalities, having been based out of multiple countries simultaneously, and conducting operations throughout the world. Their objectives affect dozens of countries with differing political systems, religions, ethnic compositions, and national interests