Dementia is a big subject and this is a big book. The first edition was edited by Raymond Levy and Alistair Burns and for this edition Professor Levy's retirement has catapulted John O'Brien and David Ames into sharing the editor's role. It is a role that seems to have been fulfilled excellently. Since the last edition the dementia field has not so much moved as leapt forward and this text valiantly does its best to keep up. To a certain extent this is an impossible task. It is simply not possible to keep abreast of the rapid developments in the fields of molecular genetics and biology. It could be argued that to do so is pointless as those who want and need to know of the latest developments will access journal or web based information. Instead, a text book, to my mind at least, should provide a repository for all those esoteric bits of knowledge, the general reviews allowing access to an area not one's own and the basic principles underlying a subject. This multiauthored text does all of those and it is those chapters that try to set out the general principles that succeed the best. Reading the chapters on topics as diverse as semantic dementia and spectroscopy was a much welcomed (and needed) educative exercise. There were many others. Not surprisingly however, the usual caveats to a text book review apply. It is expensive and, as in all multiauthored texts, some chapters are better than others. I particularly welcomed the learned chapter on the history of dementia by Berrios, the chapters on the different approaches to dementia from around the world make fascinating reading and the chapters on practical aspects such as design of environments for people with dementia and driving are excellent. One or two parts reflect more closely their author's strongly held viewpoints but diversity is always to be welcomed and this does not prevent me from concluding that this excellent book is truly an essential library purchase.