This introductory chapter sets the scene for Police Custody in Ireland, laying out the background, aim, and structure of the book. It looks at the development of detention post-arrest in Ireland, the history of miscarriages of justice, and the historic lack of structured interviewing methods and appropriate training for gardaí. It highlights significant developments, particularly from the 1970s to the present day, which will give the reader foundational context for the substantive chapters that follow.