More than 10.74 million people globally are detained in penal institutions. An estimated 40% to 90% of these detainees suffer from mental illness. This makes the prevalence of mental disorder in detainees extremely high compared with the general population (18% to 29%). As a consequence, defendants and detainees with mental illness are not 'yet another vulnerable group' that should be 'taken into account' in developing laws and policies On the contrary, they are a dominant force and therefore a factor that should shape our criminal justice systems. This edited volume provides insight into the causes of the current situation, the human rights implications and other problems that this situation generates and possible solutions and best practices. The volume comprises an introductory chapter that provides a broad introduction to the topic, seven thematic chapters addressing mental health and criminal justice from various disciplines and fourteen national chapters describing the situation in individual countries. In all these chapters a variety of questions is addressed: Should we at all put mentally ill offenders in prison? Can the human rights perspective and the interests of society perspective on this issue be united? And are mentally ill offenders the responsibility of the health department or of the justice department? This edited volume presents a thorough discussion on these and many more questions with a broader aim of contributing to a continuous effort to place the alarming situation of mentally ill offenders on the international agenda.