This systematic review aims to critically analyze and summarize the findings of peer-reviewed research studies investigating the causes, consequences, and solutions to emergency department (ED) crowding. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and searched four databases (Medline, CINAHL, EMBASE, and Web of Science) for studies published between January 2000 and June 2018. A total of 102 studies met the inclusion criteria, with the majority being retrospective cohort studies. The studies examined various aspects of ED crowding, including causes, consequences, and solutions. The negative consequences of ED crowding were well-established, such as poorer patient outcomes and staff adherence to guideline-recommended treatments. The review identified a mismatch between identified causes and solutions, with most causes related to the number and type of patients attending ED and timely discharge, while solutions focused on efficient patient flow within the ED. Solutions aimed at whole-system initiatives to meet timed patient disposition targets and extended hours of primary care demonstrated promising outcomes. However, more research is needed to isolate the precise local factors leading to ED crowding and to tailor system-wide solutions accordingly.This systematic review aims to critically analyze and summarize the findings of peer-reviewed research studies investigating the causes, consequences, and solutions to emergency department (ED) crowding. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and searched four databases (Medline, CINAHL, EMBASE, and Web of Science) for studies published between January 2000 and June 2018. A total of 102 studies met the inclusion criteria, with the majority being retrospective cohort studies. The studies examined various aspects of ED crowding, including causes, consequences, and solutions. The negative consequences of ED crowding were well-established, such as poorer patient outcomes and staff adherence to guideline-recommended treatments. The review identified a mismatch between identified causes and solutions, with most causes related to the number and type of patients attending ED and timely discharge, while solutions focused on efficient patient flow within the ED. Solutions aimed at whole-system initiatives to meet timed patient disposition targets and extended hours of primary care demonstrated promising outcomes. However, more research is needed to isolate the precise local factors leading to ED crowding and to tailor system-wide solutions accordingly.