Calcareous nannofossils are widely recognized to be a powerful tool for regional and worldwide biostratigraphic correlations. Recently, nannofossil biostratigraphy has been advanced by expanding the nannofossil database using a quantitative analytical approach, and by testing the reliability of bioevents in different time-intervals. Efforts to improve nannofossil biostratigraphy have resulted in a set of reliable "biohorizons" (biostratigraphic datums), which are correlatable across wide distances. Where dating tools such as cyclostratigraphy and magnetostratigraphy are available, calcareous nannofossil biohorizons can be used as control points for the identification of cycle numbers and polarity zones. For the Cenozoic, nannofossil biochronology can provide a basis for age models, which can then be developed into orbitally tuned cyclostratigraphies, or used for chronological revision of polarity time-scales.