This monograph is devoted to the Upper Cretaceous calcareous nannoplankton biostratigraphy in Bulgaria and the Black Sea shelf, based on many sections of various facial types, cropping out in the country: epicontinental chalk in north Bulgaria, Fore-Balkan carbonate sequences, transitional terrigenous-carbonate deposits between epicontinental and Mediterranean type in the West Balkans, limestone-marl periodites and turbidites in the East Balkans, silty-marl sequences in the Carpathian zone, terrigenous-carbonate and volcano-sedimentary sequences of the Mediterranean type Upper Cretaceous in Srednogorie zone, and chalky-marl deposits in the Black Sea shelf. The proposed nannofossil zonation includes 19 widely used zones and 15 new subzone, based on reliable nannofossil events. It does not correspond to any of the known "standard" Upper Cretaceous zonations, because none of them is entirely applicable to the territory of the country. The monograph summarizes nannofossil data from representative authors' sections and key outcrops to provide a reliable regional scheme, correlated with the most popular and widely used "standard" Upper Cretaceous zonal schemes in the world.