Marine sedimentary rocks now exposed on land are mainly deposits of shallow shelf seas, although ancient deep‐sea sediments do occur in the mountains. Thanks largely to the 15‐year effort by the Deep Sea Drilling Project of the Joint Oceanographic Institutions (JOI) Deep Earth Sampling Program, we have made quantum jumps in our understanding of the history of the ocean. Time has been added as the fourth dimension to oceanography, giving birth to a new interdisciplinary science, paleoceanography.The International Lithosphere Program is a successor to the International Geodynamics Program of the 1970s. The program is coordinated by the Inter‐Union Commission on Lithosphere (ICL), a commission of the International Council of Scientific Unions. This volume,Mesozoic and Cenozoic Oceans, is an interim report of Working Group 7 of the International Lithosphere Pr