Nationalist terrorism is a form of terrorism motivated by nationalism (often ultranationalism). Nationalist terrorists seek to form self-determination in some form, which may take the form of gaining greater autonomy, establishing a completely independent sovereign state (separatism), or joining another existing sovereign state with which the nationalists identify (irredentism). Nationalist terrorists often oppose what they consider to be occupying, imperial, or otherwise illegitimate powers.

Nationalist terrorism is linked to a national, ethnic, religious, or other identifying group, and the feeling among members of that group that they are oppressed or denied rights, especially rights accorded to others.

As with the concept of terrorism itself, the term "nationalist terrorism" and its application are highly contentious issues. What constitutes an illegitimate regime and what types of violence and war are acceptable against such a state are subjects of debate. Groups described by some as "nationalist terrorists" tend to consider themselves "freedom fighters", engaged in valid but asymmetric warfare.

Other nationalistic terrorism can include violence against immigrants in a country. Nationalists in many countries see immigration as a threat to the prosperity of the local or native population of that country.