Emergency department (ED) triage systems facilitate the categorization of emergency patients according to their disease severity and determine both treatment priority and treatment location. Four different five-level triage systems are internationally accepted. The Australasian Triage Scale (ATS, Australasia) allows categorization based on symptoms using specific descriptors. The Manchester Triage System (MTS, UK) uses defined presentational flow charts combined with indicators. The Canadian Triage and Acuity Scale (CTAS, Canada) is based on the ATS, but also includes diagnoses. The Emergency Severity Index (ESI, USA) first excludes life-threatening and severe disease before stratification according to estimated resource utilization. The goal of all triage systems is to reduce the in-hospital mortality and to minimize time to treatment, length of stay, and resource utilization.