Two rather different elements combine to explain the origin of this volume: one scientific and one personal. The broader of the two is the scientific basis-the time for such a volume had arrived. Geology had made remarkable progress toward an understanding of the phys ical history of the Caribbean Basin for the last 100 million years or so. On the biological side, many new discoveries had elucidated the distributional history of terrestrial orga nisms in and between the two Americas. Geological and biological data had been combined to yield the timing of important events with unprecedented resolution. Clearly, when each of two broad disciplines is making notable advances and when each provides new insights for the other, the rewards of cross-disciplinary contacts increase exponentially. The present volume represents an attempt to bring together a group of geologists, paleontologists and biologists capable of exploiting this opportunity through presentation of an interdisciplinary synthesis of evidence and hypothesis concerning interamerican connections during the Cretaceous and Cenozoic. Advances in plate tectonics form the basis for a modern synthesis and, in the broadest terms, dictate the framework within which the past and present distributions of organisms must be interpreted. Any scientific dis cipline must seek tests of its conclusions from data outside of its own confines.