The economic expansion following the 1973-75 recession has entered into its fourth year. Of the five previous economic expansions dated by the National Bureau of Economic Research, all but one lasted at least three years, but only one of these expansions was sustained beyond the four-year mark. The longer-run experience of U.S. business fluctuations since the end of the Civil War indicates that only three of the previous 25 business expansions lasted 16 quarters or longer, and each of these was associated with unusual circumstances such as war. As the current recovery completes its thirteenth quarter of expansion, this historical perspective brings into question whether forces are now developing which may soon end the current business expansion.