A systematic review of emergency department (ED) crowding, published in Ann Emerg Med, identifies common causes, effects, and solutions. The study analyzed 93 articles from PubMed, focusing on general ED settings and everyday crowding. Common causes include non-urgent visits, frequent-flyer patients, influenza season, inadequate staffing, inpatient boarding, and hospital bed shortages. Effects include patient mortality, transport delays, treatment delays, ambulance diversion, patient elopement, and financial impact. Solutions include additional personnel, observation units, hospital bed access, non-urgent referrals, ambulance diversion, destination control, crowding measures, and queuing theory. The review highlights the complex, multi-faceted nature of ED crowding and the need for further high-quality research to better understand and alleviate the issue. The study emphasizes the importance of addressing systemic factors, such as hospital workflow and community services, to reduce crowding. It also notes the limited use of operations research tools like queuing theory in ED settings, despite their potential to improve patient flow. The review concludes that ED crowding is a systemic issue requiring integrated solutions and further research to protect the healthcare safety net.A systematic review of emergency department (ED) crowding, published in Ann Emerg Med, identifies common causes, effects, and solutions. The study analyzed 93 articles from PubMed, focusing on general ED settings and everyday crowding. Common causes include non-urgent visits, frequent-flyer patients, influenza season, inadequate staffing, inpatient boarding, and hospital bed shortages. Effects include patient mortality, transport delays, treatment delays, ambulance diversion, patient elopement, and financial impact. Solutions include additional personnel, observation units, hospital bed access, non-urgent referrals, ambulance diversion, destination control, crowding measures, and queuing theory. The review highlights the complex, multi-faceted nature of ED crowding and the need for further high-quality research to better understand and alleviate the issue. The study emphasizes the importance of addressing systemic factors, such as hospital workflow and community services, to reduce crowding. It also notes the limited use of operations research tools like queuing theory in ED settings, despite their potential to improve patient flow. The review concludes that ED crowding is a systemic issue requiring integrated solutions and further research to protect the healthcare safety net.