-16 This is due to the grave and relevant effects that solitary confinement can cause on the mental and physical health of isolated prisoners. Solitary confinement can be found in more than one type of closed institution, such as in facilities for mentally-ill people, places of detention of migrants and, of course, in prisons. For the purposes of this handbook, the field of application will be the penitentiary system and “isolation” will be used as a synonym of “solitary confinement”. In recent years, the use of prison isolation has increased in many jurisdictions. At the same time, an increasing number of studies have highlighted the harmful effects on physical and mental health. This has led to the need for renewed action on this issue by European NPMs. The objective of this Handbook is to strengthen the capacities of European NPMs in monitoring solitary confinement and provide them greater knowledge of the phenomenon in its various aspects. Further, it wants to provide a collection of international regulations and standards on isolation, and finally to be a practical guide to the monitoring of isolation, based on the contents emerging during the seminars and interviews with different European NPMs.9 The first chapter lists and briefly analyses the different types of solitary confinement measures employed in EU penitentiary systems: disciplinary solitary confinement, isolation for preventive purposes (such as in the case of those who are considered dangerous detainees), and solitary confinement for protective purposes (as in the case of prisoners in situations of vulnerability.) The same chapter also presents a selection of the main critical issues related to the phenomenon of solitary confinement: its excessive use and the excessive duration of individual measures, the role of medical staff, the criticalities of procedural guarantees, the meaningful social contacts that would help mitigate the negative effects of solitary confinement, the frequent degradation of the cells and sections in which isolation takes place, and the banalization 9. For the purposes of this project, interviews were carried out with NPMs from Italy, France, Denmark, and Germany.