Overcrowding occurs when emergency department (ED) function is impeded, primarily by overwhelming of ED staff resources and physical capacity by excessive numbers of patients needing or receiving care. Access block occurs when there is excessive delay in access to appropriate inpatient beds (> 8 hours total time in the ED). Access block for admitted patients is the principal cause of overcrowding, and is mainly the result of a systemic lack of capacity throughout health systems, and not of inappropriate presentations by patients who should have attended a general practitioner. Overcrowding is most strongly associated with excessive numbers of admitted patients being kept in the ED. Excessive numbers of admitted patients in the ED are associated with diminished quality of care and poor patient outcomes. These include (but are not limited to) adverse events, errors, delayed time-critical care, increased morbidity and excess deaths (estimated as at least 1500 per annum in Australia). There is no evidence that telephone advice lines or collocated after-hours GP services assist in reducing ED workloads. Changes to ED structure and function do not address the underlying causes or major adverse effects of overcrowding. They are also rapidly overwhelmed by increasing access block. The causes of overcrowding, and hence the solutions, lie outside the ED. Solutions will mainly be found in managing hospital bedstock and systemic capacity (including the use of step-down and community resources) so that appropriate inpatient beds remain available for acutely sick patients.