Since it was first introduced as a separate diagnostic category, autism has been thought of as a condition of childhood. Most diagnoses, especially in lower-income countries, are still made in childhood. This chapter considers the drivers of the trend to diagnose more children: the broader boundaries of autism, the change in diagnostic thresholds and changing definitions of autism. This chapter also considers the importance of context in a child’s ability to function adequately in daily life, and the role of transition moments in provoking referrals for diagnosis and a change in a child’s diagnostic status. Finally, this chapter introduces the notion of ‘looping’, in which the category in which a person is placed leads them to reflect on themselves differently and others to treat them in a different way, which causes diagnostic categories to be revised and identities to be transformed. The chapter considers how selection bias in autism research could provoke a looping effect which, unlike the classic earlier description, does not require a person to alter their behaviour because they are so classified. The chapter discusses how such an effect might contribute to a rise in autism diagnosis.