This study presents the foraminiferal and calcareous nannofossil biostratigraphies of the three sections proposed as candidates for the Coniacian/Santonian boundary stratotype: the Olazagutía section in Spain, the Seaford Head section in England, and Ten Mile Creek section in the United States. For greater stratigraphic coverage above the boundary, the Ten Mile Creek section was combined with three stratigraphically overlying sections in Arbor Park, 34.5 km to the north. The sequence of events observed across the boundary is (in ascending stratigraphic order): the lowest occurrence of the nannofossil Lucianorhabdus cayeuxii at the base of all three sections, the lowest occurrence of the nannofossil Amphizygus minimus at the base of the Olazagutía section, the highest occurrence of the foraminifer Whiteinella paradubia in the Ten Mile Creek section, the lowest occurrence of the inoceramid bivalve Cladoceramus undulatoplicatus, the lowest occurrence of the foraminifer Contusotruncana fornicata in the Olazagutía section, the lowest consistent occurrence of the foraminifer Dicarinella asymetrica in the Olazagutía section, the lowest occurrence of the foraminifer Sigalia carpatica in the Olazagutía section, the highest occurrence of the foraminifer Sigalia deflaensis in the Olazagutía section, the highest occurrence of the nannofossil Lithastrinus moratus in the Ten Mile Creek section, and the highest occurrence of the nannofossil Amphizygus brooksii brooksii in the Ten Mile Creek section. While not perfect, with limited exposure, the Ten Mile Creek section has the best potential as the Coniacian/Santonian boundary stratotype, mainly because of the three sections proposed as potential stratotypes, it has the oldest base of Cladoceramus undulatoplicatus, based on the micropalaeontological evidence. The Ten Mile Creek section is well exposed and easily accessible, has good recovery and preservation of foraminifera, nannofossils and inoceramid bivalves, and bentonites are present that offer potential for radiometric dating. In contrast, the Seaford Head section has relatively poor nannofossil assemblages, impoverished planktonic foraminiferal assemblages, and does not appear to be suitable for correlating microfossil events to the boundary. The section does offer potential for correlating North Sea Basin benthic foraminifera to the lower Santonian stage. The Olazagutía section has moderate to good preservation of foraminifera and nannofossils, and good preservation and abundance of macrofossils, except below the lowest occurrence of C. undulatoplicatus, suggesting that this event may be environmentally controlled and the section unsuitable as a boundary stratotype. However, the Olazagutía section offers good potential for integrating the biostratigraphy of Tethyan planktonic foraminifera with that of the nannofossils of the lower Santonian.