Global calcareous nannofossil biostratigraphy is used to correlate the Paleogene chronostratigraphic units of northwestern Europe and standard nannofossil biozones. Such biostratigraphic correlations show that the lithostratigraphic sequence is discontinuous and allows interpretation of the paleogeography of northwestern Europe during the Paleogene and evaluation of the influence of global sea-level (eustatic) changes on northwestern European stratigraphy. A well-documented unconformity occurs near the lower/middle Eocene boundary in the Paris Basin. This unconformity, which also can be traced in the London-Hampshire Basin and in Belgium, correlates with a coastal offlap event (presumed sea level) of Vail et al. On the basis of magnetostratigraphic-biostratigraphic correlations, the duration of the hiatus associated with this unconformity can be estimated to be 0.6 to 1.5 m.y. in the Hampshire Basin and 2 to 4 m.y. in the Paris Basin.