In October 2011, HM Prison Birmingham was transferred from public to private management, under G4S. This was the first time that an existing operational public prison was privatised in the UK. The move marked the third and most far reaching phase of prison privatisation policy, and was intended both to increase quality of life for prisoners, from a low baseline, and to reduce costs. Prior to 2011, private prisons had all been new-builds. Private contractors had thus far avoided the additional challenges of inheriting a pre-existing workforce and operating in old, often unsuitable, buildings. This article reports on a longitudinal evaluation of the complex process of the transition, and some outcomes for both staff and prisoners. As an experiment in the reorganisation of work and life in a ‘traditional’ public sector prison, the exercise was unprecedented, and has set the agenda for future transformations. The example illustrates the intense, distinctive and rapidly changing nature of penality as it makes itself felt in the lived prison experience, and raises important questions about the changing use of State power.