This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book discusses the case of ‘disappearances’ in Northern Ireland to address a range of broader theoretical concerns. It draws on the literature of transitional justice, socio-legal studies, anthropology, criminology, memory studies, and human geography to explore the evolution of the response to this phenomenon in the Irish context. The book examines the campaigning and mobilisation work of the families of the ‘disappeared’ of Northern Ireland as an example of victims ‘doing’ transitional justice. It focuses on the Republican Movement, which perpetrated the majority of ‘disappearances.’ The book explores the broader collective memory of the disappeared in the public consciousness in Ireland and the ways in which this understanding intersects with the politics of the past. It describes the issue of the disappeared within the ongoing debates on dealing with the past more broadly in Northern Ireland and elsewhere.