‘The Master and his Emissary: The Divided Brain and the Making of the Western World’ by Iain McGilchrist
This is one of the most important books that I've read. I heard Iain McGilchrist talking about it on the radio when it was first published and just knew I had to read it. It's a weighty tome (both in size and content), covering both the structure of the brain and how the brain’s structure and function has shaped Western culture. McGilchrist is eminently suited for the task, as he taught English at Oxford University before training as a psychiatrist and is therefore able to express complex ideas in simple, attractive ways.