Since 1990, in high-income countries such as the UK and the USA, there has been an observed rise in autism diagnosis. This book considers the question: why is autism diagnosis on the rise? The introduction outlines the structure of the book and summarises the content of each chapter, briefly covering the various ‘waves’ of autism activism that have shaped how we understand autism and how, according to current medical definitions, autism is recognised using behavioural traits. The introduction establishes the book’s main standpoint: that it seeks to move beyond the somewhat tired question of whether diagnoses are ‘true’ neurodevelopmental differences or social constructions (they are both) to ask; what processes may have contributed to increased rates of autism diagnoses and is diagnosis useful?