Owing to the relative ease with which fossiliferous units can be traced into the highly metamorphosed, highly deformed terrane of southern New England, northern Appalachian orogenic events are subject to much tighter biostratigraphic control than is common in comparable areas. In most instances, for Ordovician through Early Devonian time, the precision of this biostratigraphic dating exceeds that which can be attained by isotopic dating, even for intrusive bodies. For the most part, post-Early Devonian stratigraphic control is lacking, and isotopic methods are commonly the best means of dating younger rocks and events. In spite of the good stratigraphic control and the existence of nearly 800 isotopic analyses in the northern Appalachians, fewer than 10 sets of data meet the rigorous requirements for good time-scale points. The best of these are in the late Precambrian, Middle Ordovician, Early Devonian, and Triassic time periods, where the Appalachian values agree with the commonly accepted time scales.