The impact hypothesis proposed by Alvarez and others in 1980 linked the K/T extinctions to environmental effects of a single impact. The decade of paleontological research since this proposal has shown a seemingly wide variety of extinction levels and tempos. Yet to be determined, however, is the degree to which the paleontological signal reflects actual extinction events, and how much results from stratigraphic overprint caused by hiatus, incomplete sampling, and diagenetic effects. In this chapter, four issues are addressed that seem to be central to the debate on the potential link between impact and the Cretaceous/Tertiary extinctions: the microfossil record, the effect of range truncation and sampling efforts on real vs. apparent extinction horizons, the issue of biostratigraphic “completeness,” and the possibility of a “K/T extinction precursor.”