Based on the experience of many countries in the WHO European Region and the advice of experts, this guide outlines some of the steps prison systems should take to reduce the public health risks from compulsory detention in often unhealthy situations, to care for prisoners in need and to promote the health of prisoners and prison staff. This requires that everyone working in prisons understand how imprisonment affects health, what prisoners' health needs are, and how evidence-based health services can be provided for everyone needing treatment, care and prevention in prison. Other essential elements are being aware of and accepting internationally recommended standards for prison health; providing professional care with the same adherence to professional ethics as in other health services; and, while seeing individual needs as the central feature of the care provided, promoting a whole-prison approach to care and promoting the health and well-being of people in custody.