The Emergency Severity Index (ESI) is a five-level emergency department (ED) triage algorithm that provides clinically relevant stratification of patients into five groups from 1 (most urgent) to 5 (least urgent) on the basis of acuity and resource needs. The Agency for Healthcare Research and Quality (AHRQ) funded initial work on the ESI. In 2019, the Emergency Nurses Association acquired the ESI five-level emergency triage system. Since its acquisition, ENA has focused on improving the triage learning platform to help emergency nurses better understand ESI and better identify patients who should be seen first, while prioritizing the care of patients with less urgent conditions. For more information, visit ena.org/ESI.