Although there are more than 70 species of Coccolithophoridae living in the Atlantic only about 16 of these have adequate fossil records, mainly placoliths and to a lesser extent cyrtoliths. Biogeographic ranges determined from surface sediment and plankton samples show that living species have slightly broader distributional ranges than those preserved in oceanic sediments. This is attributed to rapid warming of the Atlantic since the last glacial age. Species distributions have been delineated by maximum position poleward of the limiting isotherm for warm-water species and maximum equatorward position of the limiting isotherm for cold water species. Dispersion beyond their present boundaries by ocean currents after death is negligible. Temperature studies based on cruise data and bimonthly sampling off Bermuda enabled the authors to determine maximum and optimum temperature ranges for each species. The majority are subtropical forms. A few are stenothermal, such as Umbellosphaera irregularis (21°-28°C) and Coccolithus pelagicus (7°-14°C) and they have proved useful in paleoecology. The species are grouped into five climatic assemblages: tropical, subtropical, transitional, subarctic, and subantarctic.