Despite increasing efforts to tackle human trafficking (or ‘modern slavery’), the evidence base is notoriously limited. This introductory chapter turns the spotlight on an important but long-overlooked form of trafficking: internal trafficking for child sexual exploitation. It explains how this problem came to be associated in the UK with so-called ‘street grooming’ and ‘Asian sex gangs’. Emergent myths and their flaws are highlighted. The international literature is reviewed, with a focus on the UK, US (‘domestic minor sex trafficking’) and Netherlands (the ‘loverboy’ phenomenon). The chapter sets out the new research behind this book, which is designed to identify factors underpinning this crime and impeding official responses. A case study approach is introduced based on six of the UK’s earliest and largest investigations, including the now infamous Rochdale case. This book is shown to offer readers a rare opportunity to explore the hidden world of offender and victim networks, addressing their composition, structure, activity and dynamics and the challenges they pose for investigation and prosecution. An innovative combination of methods and unique set of hard-to-access data sources support a nuanced exploration of a complex and challenging problem.