In recent years, correctional agencies across Australia have been increasingly influenced by the model of rehabilitation commonly known as the “what works” approach to offender rehabilitation. The “what works” approach is a core set of principles of human service delivery. These principles suggest that reductions in recidivism can be maximized when programs select candidates, target factors that directly relate to their offending, and facilitate learning. It is a model of differentiated case management, whereby those with the highest level of need and greatest risk of reoffending are given the most intensive programs. These core principles include: risk principle, needs principle, responsivity principle, integrity principle, and professional discretion principle. In recent years, juvenile justice agencies across Australia have become interested in applying these core principles to programs delivered with juvenile offenders. This paper describes and explains each of five core principles in relation to juvenile justice services and programs. References