The product of an 8-year research study, this book presents a complete and detailed overview of autism/ASD which draws together both psychological and physiological aspects from the current research base, to present a novel and logical theory of what autism really is and why it occurs. It concludes by providing answers to many commonly asked questions about autism/ASD. The layout of the book follows my personal journey through the autism/ASD literature: Chapters 1-5 each present the current research base on five different aspects of the field. Chapters 6-8 explore a range of environmental factors over three life time-scales. In Chapter 9, I generate an ecological model within which to understand autism/ASD, and in Chapter 10 examine the potential role of genes. Chapter 11 provides a stand-alone summary of the data reviewed so far with salient points identified. The hypothesis itself is presented in Chapter 12. An explanation for the triad of impairments and other characteristic behaviours of autism/ASD is offered in Chapters 13 and 14, while Chapter 15 addresses some commonly proposed questions about autism/ASD in the light of this new theory.