For many years, researchers have utilized definitions of the substorm phenomenon that are not consistent among one another, and this has created great difficulties in comparing the results reported in the literature by the various researchers. In August 1978, nine magnetospheric physicists active in the field of substorm research met in Vicotria, British Columbia, Canada, to attempt to reach a consensus on an acceptable definition for a magnetospheric substorm. This paper reports the agreements reached at the Victoria workshop and presenta an operational definition of the magnetospheric substorm and a critique of the various signatures by which researchers can identify the time sequence and spatial extent of the substorm.