The U.S. Geological Survey stream-gaging program provides streamflow data for a variety of purposes. The uses of streamflow data are described, and the growth of the stream-gaging program is related to legislation and the need to manage the Nation's water resources more effectively. A brief description is provided of the data-collection processes, computation of streamflow records, dissemination of data, and the nationwide evaluations of the stream-gaging program. Finally, the challenges for maintaining a viable stream-gaging program are described.