Don't bring me your tired, your poor: the crowded state of America's emergency departments.

If the time comes, people expect that the emergency department (ED) will have the resources necessary to treat them in a timely, high-quality manner. Increasingly, however, EDs may not be able to meet that expectation. Hospitals in urban areas with large populations, high population growth, and higher-than-average numbers of uninsured are particularly crowded: ambulances are often diverted to other hospitals and patients are frequently forced to "board" in the hallways (while they wait to be transferred to another facility or part of the hospital). This issue brief places EDs in the context of the U.S. health care system and its economics, discusses existing ED capacity and utilization, where crowding is happening and ways of measuring it, what is causing crowding in EDs, and the consequences of crowding. It highlights a number of potential ways to alleviate crowding at both the health system and the individual hospital level.