The diagnosis of autism in adulthood is a relatively new practice, which our analysis shows has been rising quickly in England since 2010. The rise in diagnosis is partly due to greater availability of diagnostic services (especially in the UK) and partly to a range of activities around autism that raise its profile, including ‘autie-biography’ – first-person autobiographical accounts that people can draw on to recognise themselves. Many people diagnosed in adulthood have the means, methods and motivation to mobilise. Such autistic activism, emerging in the 1990s, formed the basis of the neurodiversity movement. The movement argues that autism is a valuable and natural part of human variation, not a disorder but a different way of being, broadly opposing eradication or cure of autism. The chapter will describe the rising influence of autistic identity, the concept of being ‘autistic’ versus the medical position of ‘having autism’, shining a light on the work of the movement to de-stigmatise autism, the net effect of which is to make it more likely adults and parents will self-identify and adopt the label in the future. This provides another example of a looping effect.