Monitoring the use of isolation is an important part of prison monitoring -9 Prison Rules (EPR) and other standards set by international human rights bodies. The contents of the third chapter are a practical guide to monitor isolation. It is based on good practices that emerged from interviews and meetings with NPMs and experts, with particular attention to physical visits to the penitentiary institute. It is divided into phases (preparation of the visit, carrying out of the visits, follow-up) and, like the other chapters, into thematic subchapters (study of prison registers, role of doctors, interviews, material conditions, etc.) The specific monitoring of solitary confinement requires the widest possible collection of information prior to the visit. The handbook explains how some NPMs collect them. The handbook also illustrates the various moments and aspects of the visit. The first step to identify any critical issues related to isolation consists of the examination of prison records/registers on sections, critical events, disciplinary measures, medical records (collective or individual medical records) and the individual file of the detainee. The study of records can reveal the average duration of the isolation measures, as well as show if the isolation of detainees is mitigated by meaningful social contacts, what type of contacts they are, and who carried them out. Prison Monitoring Solitary Confinement in Prison