-17 of having their basic human rights violated. Prisoners in a situation of vulnerability require positive measures and particular services on part of the authorities to meet their special needs and/or to ensure their protection. Some persons are vulnerable in prison for the same reason for which they are vulnerable outside prison. But in many other cases certain factors may render – depending on the contexts of the imprisonment – some groups of prisoners specifically vulnerable. Thus, it is advised to use a broad and open concept of vulnerability. Various personal, environmental or sociocultural factors could cause a specific vulnerability in individual prisoners. There are vulnerabilities of more permanent chronic character and those that are more temporary. A combination of several risk factors may lead to multiple or intersectional vulnerabilities, which requires authorities to pay special attention, given the multiple risks someone might be exposed to. Exploring the risk factors for vulnerability should be one of the primary tasks of the prison management already from the first day of detention and should continue throughout the period of imprisonment. The purpose of this handbook is to explore in-depth the challenges with the treatment of the prisoners in a situation of vulnerability and the approaches to address them through preventive monitoring. We analyse the situation at the EU level, the existing international standards related to groups in a vulnerable situation in prisons and the approaches of the NPMs to promote the rights of these groups in the exercise of their preventive functions. The handbook also offers practical guidance to monitoring of the rights of groups and persons in a situation of vulnerability in detention. Prisoners in a Situation of Vulnerability