A territorial dispute or boundary dispute is a disagreement over the possession or control of land between two or more political entities.

Irredentism is one state's desire to annex the territory of another state. This desire can be motivated by ethnic reasons because the population of the territory is ethnically similar to the population of the parent state. Historical reasons may also be responsible, i.e., that the territory previously formed part of the parent state. However, difficulties in applying the concept to concrete cases have given rise to academic debates about its precise definition. Disagreements concern whether either or both ethnic and historical reasons have to be present and whether non-state actors can also engage in irredentism. A further dispute is whether attempts to absorb a full neighboring state are also included. There are various types of irredentism. For typical forms of irredentism, the parent state already exists before the territorial conflict with a neighboring state arises. However, there are also forms of irredentism in which the parent state is newly created by uniting an ethnic group spread across several countries. Another distinction concerns whether the country to which the disputed territory currently belongs is a regular state, a former colony, or a collapsed state.