Experience shows that torture and ill-treatment usually occur when people are deprived of their liberty, although torture and ill-treatment are explicitly prohibited in (inter)national law. This led to the establishment of international monitoring bodies, which prevent ill-treatment through a system of visits and negotiations with relevant authorities. Their succes led to the adoption of the UN Optional Protocol to the Convention Against Torture (OPCAT), which was considered groundbreaking for establishing similar preventive bodies at the national level, called National Preventive Mechanisms (NPMs). However, policy documents show that significant differences exist between NPMs and that the track record of several NPMs is far from perfect. 10 Years after the OPCAT’s entry into force, focus should shift from research on the organisational prerequisites for the functioning of NPMs, to their actual functioning in practice, as to clarify whether NPMs can be considered successful or whether the OPCAT remains a paper tiger. This research analyses the operation of NPMs in law, policy and practice, with regard to their mandate, assessment framework and priorities in FR, NL and the UK. The answers aim not only at understanding the functioning of different NPMs but equally offer a comparative view on NPMs in different European countries as, although the prohibition of torture is universally recognised, the actual protection against torture differs substantially between countries.