The assessment of criminal behaviours of clients in secure settings poses a number of particular problems; the behaviour in question is neither currently evident, nor can it ethically be elicited. This results in a great reliance on official records and self-report, with the inevitable attendant problems of validity. Notwithstanding this, assessment is used for making critical decisions about a person's liberty and treatment, providing information for courts before sentencing and identifying strategies to be written into sentence plans and treatment plans. Recognising the assessment of criminal behaviour to be a complex and important skill, this text draws from a wide range of professional experience to give guidance to prison officers, probation officers and social workers, as well as psychiatrists and psychologists who are involved in the assessment of criminal behaviour. Report writing and the presentation of information in court, both of which form part of the important task undertaken by the professionals involved, are explored in separate chapters.