Registered nurses (RNs) are the single largest group of health care professionals in the United States. Current and projected nursing shortages reflect the fact that fewer people are entering the profession. Shortages are difficult to estimate and project. In the past, shortages have tended to be resolved as wages rose in response to increased need for RNs. In addition, there is a cyclical aspect to shortages, as RNs are more likely to work when the economy is doing less well. Projected shortages differ from past circumstances in that, by 2020, a decline in the number of available nurses will coincide with an increased need for nursing services due to aging of the baby boom generation. These changes suggest that it will be more difficult, and more costly, to respond to the future shortage.