The present study was conducted through a review of triage in disasters and mass casualty incidents, with the aim of identifying triage systems, relevant criteria, and the order of these criteria all over the world. The triage system is used by individuals to determine which groups of the patients should receive treatment and care services based on their clinical status, the prognosis of disease and available resources. This step will be done by a surgeon or a critical care specialist. The third triage is performed to prioritise and decide on receiving care services, including transferring to the operating room or the intensive care unit. In these cases, triage will be done by an emergency doctor or surgeon as soon as the injured person arrives at the hospital. Secondary triage which is used when, due to the large extent of the incident and lack of resources in the pre-hospital, the transmission of the injured person has been prolonged in the scene. Triage is usually performed at three stages: the primary triage that is carried out at the scene of the incident by an emergency technician aims at the prompt assessment of the injured person and rapid transfer to the treatment center. The process of triage allows the respondents of disaster, who do not have enough resources to treat everyone, to prioritize care services, so that most services are provided to the greatest number of injured people, and this is essentially the philosophy of doing triage in disasters and mass casualty incidents. Triage is derived from the French word “trier”, which means separating, categorising or classifying, and refers to the categorization, classification, and prioritization of patients and injured people, based on their urgent need for treatment. Triage is one of the key principles of the effective management of major emergencies. Although the concept of triage applies to all resources, “patient care” is the most commonly discussed field for which the notion of triage is used. Triage is the allocation of limited resources during a disaster. One of the symptoms of disasters is that the immediate needs of the community affected exceed the available resources, so the question is how these resources should be used to have the best outcome for the people.