As the Dutch TBS order aims to prevent dangerous (mentally disordered) offenders from re-offending through confinement and treatment, it is of indeterminate duration. As a consequence, its legitimate imposition and execution depend both on legal safeguards and behavioural science evidence. A fortiori, the uncertainty of behavioural science evidence calls for specific legal safeguards itself. This also applies to comparable sanctions in other jurisdictions. The proposed research therefore examines the question: How can the indeterminate sentencing of dangerous offenders be made more legitimate, both legally and empirically? Divided into four sub-questions, the research will lead to several papers in preeminent international journals in the field of law and behavioural science. Firstly, indeterminate sentencing will be tested with regard to the legal state of the art through a comparison of the provisions in six Western jurisdictions and an analysis of subsequent constitutional or human rights-related case law. Secondly, the provisions for indeterminate sentencing in these jurisdictions will be confronted with the behavioural science state of the art as derived from empirical evidence. This is called for as some sentences have existed for many decades and others have been based on single incidents, while all use behavioural scientifically challenged criteria such as dangerousness, disorder, criminal responsibility, and treatability. Thirdly, procedural provisions on the use of behavioural scientific evidence in the six jurisdictions will be compared. As the jurisdictions are equally divided amongst inquisitorial and adversarial legal systems, the consequences of having either a univocal testimony or a ?battle of the experts? will be discussed. Fourthly, these procedural provisions will be tested empirically with a view to determining which legal safeguards deal most effectively with the uncertainty of behavioural science evidence. The final aim is to form both nationally and internationally applicable interdisciplinary standards (or recommendations) for legitimate imposition and execution of indeterminate sentences.