In the Republic of Croatia and other European countries, the Unified Emergency Department (UED) is the place where a large number of patients seek emergency medical care. In order to effectively manage this department, a triage system is used as a fundamental tool. The main purpose of triage is to categorize patients according to urgency and ensure timely assessment of all patients arriving at the UED. Based on the patient's clinical condition, triage determines the level of urgency required to achieve the best possible outcome. A standardized and structured triage process is an important tool for assessing the quality of work in any Unified Emergency Department. In the Republic of Croatia and worldwide, a five-level triage scale is used, and one of the most significant ones is the Australasian Triage Scale (ATS). ATS stands out for its use of physiological indicators and focused clinical history to classify patients' symptoms into appropriate triage criteria. This scale enables a structured assessment of the patient, taking into account vital functions, symptom severity, and other relevant factors. The use of ATS allows healthcare professionals to objectively assess the urgency of a patient's condition. Based on physiological measurements such as respiratory rate, blood pressure, pulse, level of consciousness, and clinical history, patients' complaints are categorized into the appropriate triage level. This allows healthcare professionals to determine the order of patient care and provide prioritized treatment to those with the most urgent conditions. Triage in emergency medical services does not necessarily require the presence of a physician; it can be performed by a well-educated and motivated nurse or paramedic. The role of the triage nurse is multifaceted. They are the first point of contact for patients upon arrival at the Emergency Department, and successful communication with the patient has a significant impact on further collaboration with the patient and their family. Therefore, it is crucial for the triage nurse to possess good education, the ability to recognize patients' difficulties, and the capability to determine the appropriate triage category for each patient. Additionally, they must be skilled in communication. The triage nurse is responsible for the care of every patient in the Emergency Department waiting area until they are handed over to a physician or another nurse in the hospital ward. Their role is to ensure patient safety, monitor their condition, provide basic care, and be available to provide emergency assistance if needed. This paper will present the concept of triage and why it is a fundamental tool in managing the Unified Emergency Department. It will discuss the triage scales and categories used, as well as the purpose of the triage system in the context of providing acute healthcare. Furthermore, it will outline the role and responsibilities of the triage nurse and the necessary knowledge they must possess to ensure a smooth triage process and provide appropriate and timely assistance to patients. The paper will also address specific aspects of triage in pediatrics, gynecology, psychiatry, and mass casualty incidents.