In the field of penology, rehabilitation is usually specified by courts of law as one of the objectives of sentencing, alongside retribution, incapacitation, deterrence and restoration. The long-held consensus regarding the possibility of rehabilitation was questioned during the 1970s as a result of claims that there was no evidence that any kind of intervention had proven effective in reducing subsequent reoffending. Rehabilitation effect sizes are larger for adolescent and for adult offenders. Rehabilitative endeavours are most likely to succeed when they are based on a theory of criminal behaviour that is conceptually clear and has firm empirical support. Rehabilitative efforts work better if they have clear, concrete objectives, their contents are structured, and there is a focus on activity and the acquisition of skills. Personnel involved in delivering them should possess high-quality relational skills and foster supportive, collaborative working within clearly defined boundaries.