Imagine the following three offenders: The first is a violent offender. He has committed a number of violent offences like robbery, grievous bodily harm, or attempted murder. Right after his release from prison, he committed another offence and therefore spent most of his life in prison. The second offender committed a series of rapes and sexual assaults on girls. He takes photographs and films the abuse. The third offender committed only one, but very dreadful offence. He developed a sexual interest in his own two-year old son whom he then raped causing very serious harm to the boy. In all these cases, the courts found that the offender was a serious risk to the public because of a certain tendency (the German provisions use the word “propensity”) to commit further offences and therefore poses a constant threat to society. This thesis aims to present the way the penal system deal with this specific kind of persistent, dangerous offenders in Germany, England and Wales. The group exists in every society and different approaches have been taken to protect the public. The need to deal with these offenders reaches back to the roots of mankind and early penalties included death penalty, deportation to colonies and servitude on galleys. Yet, eventually indeterminate imprisonment replaced all of the former penalties and is still used today in England and Germany. The English preventive sentence consists of an often undetermined sentence, which already includes a determined period appropriate for the gravity of the most recent offence (minimum term). On the other hand, the German system combines two differing sanctions, usually imposed in one judgement. One determined sentence and one indeterminate incapacitation order, the so-called Sicherungsverwahrung. The first term serves as retribution and is determined taking the seriousness of the offence into account, while Sicherungsverwahrung is not seen as a penalty, but a measure to protect society from dangerous offenders. It is consequently indeterminate and will last as long as the offender posses a threat to the public.