ObjectivesWhat happens to those who are called serious criminals once the conviction has been handed down and the possibilities for appeal exhausted; and, first and foremost, what is meant by the term serious criminal? Is this only the penal qualification of a criminal conviction, or should it be combined with the length of the sentence? Is the repetition of criminal acts a condition for this designation, or is the “simple” sentence of life imprisonment, whatever the reason for the sentence, sufficient? MethodsThrough the examination of the various legislative developments and the confrontation between different players in the judicial system, the future of these subjects is put into perspective. ResultsThe difficulty of finding a single definition of the concept of serious criminality illustrates, on its own, the diversity of profiles and individual situations it covers. However, given the sociology of long-term prisoners, the combination of three criteria, excluding the repetition of criminal acts, seems relevant to the definition of the concept of a serious criminal: the sentencing of the individual, male or female, a sentence of at least 15 years, the assignment of the convicted individual to a penal institution, whether a jail, a prison, or a maximum security prison. The definition criteria therefore exclude the nature of the acts that led to the conviction, the question of repeat offenses in the commission of criminal acts, as well as the age group to which he belongs. As of July 1, 2018, according to figures from the French prison administration, 500 prisoners were serving a life sentence, 1,000 prisoners were serving a criminal sentence of more than 20 years, and 5,200 prisoners were serving a criminal sentence of more than 10 years, out of a total number of 71,000 prisoners. DiscussionFor these serious criminals, how can we reconcile the objectives set by the law with regard to the function assigned to the prison sentence – namely to prepare the integration or reintegration of the convicted person in order to enable him to act as a responsible person, respecting the rules and interests of society and avoiding the commission of new offenses – with the crucial question of dangerousness in the case of serious criminals? Whether or not the convicted person is considered a major criminal, the objective of the prison journey must remain the same: to allow a safe return to civilian life from the point of view of society and to provide security for the convicted person. This secure return will be made possible if all the parties involved (the prefectoral authority, the judge in charge of enforcing sentences, representatives of the public prosecutor's office, integration and probation prison counsellors, coordinating doctors) work in concert, the challenge in terms of public safety being essential. ConclusionTo talk about the future of serious criminals requires, after the relatively unknown question of the management of detention, that we look at the question of the adjustment of the sentence. Recent criminal procedural reforms, which have focused on combating prison overcrowding and limiting the imposition of short prison sentences, have had relatively little impact on those sentenced to very long sentences. The treatment of serious criminals in detention and then at the sentencing stage has its own specific features. The objectives sought are first of all those common to all persons serving a sentence of imprisonment or criminal confinement, namely the prevention of recidivism and the rehabilitation of the convicted person, objectives set out in article 707 of the French Code of Criminal Procedure. Follow-through with serious criminals in the event of a return to civilian life also deserves attention because it differs from the way other cases are handled.