It is an odd assignment, this one: not as a non-neuroscientist the request to write a review of a book on the structure and functioning of the left and right hemispheres of the brain, for The master and his emissary is after all aimed at the intelligent general reader, and in this context I can at least lay claim to being a general reader; but rather the invitation to make such an assessment for a journal whose readership is largely confined to neurologists and neuroscientists, an audience whose expertise on the underlying brain science is orders of magnitude greater and more sophisticated than mine. How to tackle such a task? It makes no sense for me to devote much space to a critique of Iain McGilchrist’s mastery of the research literature on which he draws to make his case, for there are literally thousands of reviewers more competent than I to undertake such an assessment. Instead, like other non-specialist readers, I must perforce take largely on trust his claims to represent the current state of neuroscientific knowledge, and will turn most of my attention elsewhere: to where his analysis sits in a long-running historical debate on the duality of the brain; and to an examination of his attempt to move from the narrow findings of neuroscience to a remarkably bold and ambitious attempt to understand their implications for, as he puts it in his subtitle, ‘the making of the Western world’. ![Graphic][1] That human and mammalian brains are composed of two hemispheres has long been known. Greek physicians from the third century before the Christian Era knew of and speculated about the divided brain, and McGilchrist mentions, largely in passing, that Galen’s anatomical researches, mostly conducted on animals, made this basic duality of the brain known to all interested parties from … [1]: /embed/inline-graphic-1.gif