The Pleistocene Boundary and the Beginning of the Quaternary presents the results of a forty-year international program to establish a precise definition for the most important boundary in geologic time - the beginning of the modern age of glacial climates. This book, the final report of International Geological Correlation Project 41, describes the selection of a fixed reference point in the sequence of deep-water marine strata exposed at Vrica, Italy. This point, dated to 1.81 million years before the present, coincides with the onset of the first of four major glacial phases. The opening chapters of the book document the geology and palaeontology of the agreed physical reference point, and the successful proposal of this point as the boundary-stratotype of the Pleistocene Epoch. The book then describes the correlation of the boundary throughout the ocean basins and continents of the world in terms of detailed stratigraphic criteria such as planktonic biostratigraphy, magnetostratigraphy and radiometric age determinations.