In international relations, the security dilemma refers to a common situation wherein two or more states are drawn into conflict, possibly even war, over security concerns when none of the states involved actually wanted conflict.

Essentially, the security dilemma occurs when two or more states each feel insecure vis-à-vis other states that they do not trust. None of the states involved want war, or even lesser forms of conflict; however, because none of the states feel secure and none of the states trust the other states to not take aggressive actions, the states involved build up their military forces or take other actions that provoke the other state or states. Each such provocation results in an escalation of conflict leading to the next provocation, until open war is the final result. The irony is that none of the states were interested in going to war in the first place.

An example often cited of the security dilemma is the beginnings of World War I. Supporters of this viewpoint argue that the European states felt forced to go to war by feelings of insecurity at the alliances of other states when none of the states really wanted war. However, some scholars dispute this, contending that the states involved really did want to go to war.

The security dilemma is a popular concept with cognitive and constructivist theorists of international relations, who regard war as essentially arising from failures of communication. Cognitive theorists affirm that the key to avoiding war is the avoidance of miscommunication through proper signaling.