The first edition of this book was conceived with the intention of providing a practical guide to the neuropathological diagnosis of dementia. It was intended particularly for those who did not regard themselves as experts in this increasingly complex field. The relatively small number of authors was encouraged to share their diagnostic experience with others. This second edition still aims to provide practical assistance in this way, but it now goes further than that. The pace of scientific research advances in this field of dementia is such that it has become a formidable enough task for an expert to remain fully conversant with his or her own subfield, let alone with the field as a whole. Therefore we have aimed to widen the authorship greatly so that many chapters could be written by those specialists with research interests in the topic that is covered by each. We are delighted that those approached have responded so generously and enthusiastically since the outstanding contributions from the authors have made the second edition the most up-to-date and comprehensive monograph on the neuropathology of dementia. Because of the wider international authorship it has also been possible to extend the scope of the coverage of each topic to include more about research findings and the background science so that the book can now claim to provide comprehensive coverage of current understanding of the dementias rather than a more restricted practical guide. We hope, therefore, that a wider readership of neurobiologists and clinicians as well as pathologists will find much of interest here. Those familiar with the first edition will find that there are many new chapters and even more new authors contributing to the second edition.