This briefing paper is based on an examination of good or promising practices in services for people at each stage of the criminal justice system across England. It describes the key features of those services and then distils the core components of effective support for people with personality disorder in or around the justice system. Finally, the paper sets out some keys to effective engagement from the insights gained from the good practice sites. Two-thirds of prisoners and about half of people under probation supervision are estimated to have personality disorder traits, yet only a small proportion get any support. The paper commends the national Offender Personality Disorder Strategy which is extending support to more people in prison and outside whose personality disorders are linked to their offending. This has led to the creation of psychologically informed physical environments (PIPEs) in prisons, where staff have received training in working with people with a personality disorder, where treatments are offered and where relationships between staff and prisoners are key to success. The briefing paper calls on health and criminal justice services to work together to ensure effective interventions are offered at every stage of the criminal justice system to all offenders with a personality disorder.