In 2010, the prison population in England and Wales could reach a high of 91,500, according to a recent population projection. HM Prison Service (U.K.) reports that in 2004 to 2005, there were 33,144 prison officers employed to care for the prisoners in the prison system. This article focuses on the mental health of this prisoner population and the training needs of staff caring for them. It reports the experience of a national project, funded by the Department of Health, in which the project team developed and piloted mental health awareness training for prison officers on the residential units and for staff who work with prisoners and lack a mental health background. Key findings from the posttraining evaluation are highlighted. Participant feedback demonstrates the value placed on this type of training by those working in the prison setting.