-15 thematic areas.6 The research began after a brief initial consultation with NPMs to refine the project focus.7 Within the framework of the Project, several consultations took place. Representatives of NPMs and other experts exchanged experiences and best practices at four workshops - one per each thematic issue - as well as in a final conference, which took place on 3 and 4 November 2020.8 In addition, each Project Partner conducted several bilateral interviews with representative of NPMs, as well as other national or international experts and practitioners. The Project findings resulted in four thematic Handbooks. While there are strong interlinkages between them, the Consortium found it necessary to have four separate Handbooks in order to address the specific international standards and monitoring challenges for each thematic issue in depth. Accordingly, each Handbook was authored by the staff of the respective Project Partner. Introduction to the Handbook This handbook aims at supporting the work of the national preventive mechanisms (NPM) in the European Union (EU) in monitoring the rights of persons and groups in a situation of vulnerability. Article 1 of the Optional Protocol to the Convention against Torture and other Cruel, Inhuman or Degrading Treatment or Punishment (OPCAT), the treaty on the basis of which the NPMs were established, provides for the establishment of a system of regular visits undertaken by independent international and national bodies to places where people are deprived of their liberty, in order to prevent torture and other cruel, inhuman or degrading treatment or punishment. Effective prevention of such practices presupposes targeting them through visits to places where they are most likely to occur 6. The Project covered 22 EU Member States. 4 EU Member States (Belgium, Ireland, Latvia and Slovakia) were not covered because they have not yet ratified the OPCAT; 2 EU Member States (Denmark and the United Kingdom) were not covered because they do not to participate in the European Commission Justice Programme. It is also worth noting that the United Kingdom withdrew from the EU on 31 January 2020 and therefore since 1 February 2020 is no longer an EU Member State. 7. The online survey was conducted in March 2019. 14 out of 22 NPMs participated. 8. The first Workshop “Treatment of certain groups of prisoners in a situation of vulnerability” took pace in Sofia on 18 – 19 November 2019; the second Workshop “Isolation and solitary confinement in prison“ took place in Rome on 27 – 28 January 2020; the third Workshop “Requests, complaint procedures and the right to information in prisons” took place online due to the Covid-19 pandemic on 27 – 30 April 2020; the fourth Workshop “Preventive Monitoring of Violence in Prisons” took place also online on 20, 27 May and 3 June 2020. Moreover in July 2020 an online consultation on the Systemic Approach to NPM work was held. Prisoners in a Situation of Vulnerability