A ceasefire (or truce), 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. Historically, the concept existed at least by the time of the Middle Ages, when it was known as a 'truce of God'. Ceasefires can be declared as a humanitarian gesture, be preliminary, i.e., prior to a political agreement, or definitive, i.e., with the intention of resolving a conflict. Ceasefires may be declared as part of a formal treaty, but they have also been called as part of an informal understanding between opposing forces.Ceasefires may be between state actors or involve non-state actors. They may be formal (usually written), or informal; their conditions may be public or secret. Ceasefires 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.A ceasefire is usually more limited than a broader armistice, which is a formal agreement to end fighting. Ceasefires may be abused by parties as cover to re-arm or reposition forces, and they typically fail, when they are referred to as 'failed ceasefires'; however, successful ceasefires may be followed by armistices and then by peace treaties.

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.