Emergency department (ED) crowding is a significant global healthcare issue with complex causes and consequences. This systematic review analyzed peer-reviewed studies from 2000 to 2018 to identify the causes, consequences, and solutions to ED crowding. The review included 102 studies, with 51% focusing on potential solutions, 14% on causes, and 40% on consequences. The majority of studies were retrospective cohort studies, and most were from the USA, Australia, and Canada. Key findings include that ED crowding leads to poor patient outcomes, increased inpatient length of stay (IPLOS), higher inpatient mortality, and negative impacts on staff, including increased stress and exposure to violence. Causes of crowding include increased patient numbers, especially among the elderly with complex conditions, low-acuity presentations, and poor access to primary care. Solutions include improving access to primary care, increasing ED bed numbers, and implementing timed patient disposition targets. The review identified a mismatch between causes and solutions, with most solutions focusing on improving patient flow within the ED rather than addressing systemic issues. Solutions such as whole-system initiatives, extended primary care hours, and improved bed management showed promise. However, many studies had limitations, including inadequate consideration of confounders and basic statistical analysis. The review highlights the need for more research to isolate local factors contributing to ED crowding and to develop system-wide solutions tailored to specific causes.Emergency department (ED) crowding is a significant global healthcare issue with complex causes and consequences. This systematic review analyzed peer-reviewed studies from 2000 to 2018 to identify the causes, consequences, and solutions to ED crowding. The review included 102 studies, with 51% focusing on potential solutions, 14% on causes, and 40% on consequences. The majority of studies were retrospective cohort studies, and most were from the USA, Australia, and Canada. Key findings include that ED crowding leads to poor patient outcomes, increased inpatient length of stay (IPLOS), higher inpatient mortality, and negative impacts on staff, including increased stress and exposure to violence. Causes of crowding include increased patient numbers, especially among the elderly with complex conditions, low-acuity presentations, and poor access to primary care. Solutions include improving access to primary care, increasing ED bed numbers, and implementing timed patient disposition targets. The review identified a mismatch between causes and solutions, with most solutions focusing on improving patient flow within the ED rather than addressing systemic issues. Solutions such as whole-system initiatives, extended primary care hours, and improved bed management showed promise. However, many studies had limitations, including inadequate consideration of confounders and basic statistical analysis. The review highlights the need for more research to isolate local factors contributing to ED crowding and to develop system-wide solutions tailored to specific causes.