-15 standards related to the four thematic issues, as well as on how EU NPMs monitor and contribute to the development of the standards in these 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 Solitary confinement can be broadly defined as the separation of a detainee from the general prison population. The prisoner is housed alone in a cell for the greater part of a day; international standards usually indicate 22 hours as the minimum to consider a situation as solitary confinement. However, it is important to highlight that there is no unique definition for this practice, and that different human rights bodies approach the issue of the definition of solitary confinement in different ways. International human rights bodies, especially those involved in the fight against torture, place solitary confinement at the top of their priorities. 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 Goal” 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. Monitoring Solitary Confinement in Prison