The Global Standard Stratotype-section and Point (GSSP) concept is the modern standard for defining chronostratigraphic units in the geological time scale, and over the past decade the working groups involved in locating and characterizing GSSPs have rekindled appreciation for stratigraphy within the profession. The rules adopted hy the ICS for establishing the GSSP are, however, less restrictive than, and to some extent in conflict with, the principles set forth by the international Subcommission on Stratigraphic Classification (ISSC) under the leader-ship of Hollis Hedberg (1976). Under the ICS rules, global boundaries may he established ad hoc for units at any level without regard for the constraints of nested chronostratigraphic hierarchy, even while acknowledging that the stage supposedly holds the critical place. Furthermore, the ICS rules, in advocating that GSSPs be located strictly according to their correlatibility, have the effect of requiring preconceived boundaries that cor respond to global geohistorical events. These apparently practical shortcuts have serious consequences against which the Hedherg guidelines specifically, warned. Not only does the disregard of stage unit- and boundary-stratotypes do more or less violence to the existing literature, but event-based definitions are inherently unstable in stratigraphic space. We review here the problems associated with the definition of a GSSP, using the controversy over the Paleocene/ Eocene boundary as a case history.