A ceasefire (also known as a truce or armistice), also spelled cease fire (the antonym of 'open fire'), is a temporary stoppage of a war in which each side agrees with the other to suspend aggressive actions. Ceasefires may be between state actors or involve non-state actors.

Ceasefires may be declared as part of a formal treaty, but also as part of an informal understanding between opposing forces. They may occur via mediation or otherwise as part of a peace process or be imposed by United Nations Security Council resolutions via Chapter VII of the United Nations Charter.

The immediate goal of a ceasefire is to stop violence, but the underlying purposes of ceasefires vary. Ceasefires may be intended to meet short-term limited needs (such as providing humanitarian aid), manage a conflict to make it less devastating, or advance efforts to peacefully resolve a dispute. An actor may not always intend for a ceasefire to advance the peaceful resolution of a conflict, but instead give the actor an upper hand in the conflict (for example, by re-arming and reposition forces or attacking an unsuspecting adversary), which creates bargaining problems that may make ceasefires less likely to be implemented and less likely to be durable if implemented.

The durability of ceasefire agreements is affected by several factors, such as demilitarized zones, withdrawal of troops and third-party guarantees and monitoring (e.g. peacekeeping). Ceasefire agreements are more likely to be durable when they reduce incentives to attack, reduce uncertainty about the adversary's intentions, and when mechanisms are put in place to prevent and control accidents from developing into conflict.