Introduction: the paper deals with the doctrinal principle of the inevitability of punishment and focuses on the possibility of implementing it in legal relations under penal enforcement law. The purpose of the paper is to identify how this interdisciplinary principle is respected in the enforcement of criminal sentences, and to propose mechanisms for its implementation. The study employs such methods as description, observation, statistical analysis, documentary analysis, induction, analogy, and thought experiment. Results: the paper reveals the fact that within the existing system of measures of negative and positive impact on the behavior of convicted persons, it is practically impossible to ensure the principle of the inevitability of punishment being implemented when it comes to sentences that are not related to isolation from society. Implementation of this principle in the execution of punishments related to isolation from society is not of legal but of organizational nature. Conclusions: the inability to execute a punishment in strict accordance with the requirements of the law leads to the loss of the deterrent value of punishment. When punishment is not related to isolation from society, convicts do not seek to serve the imposed punishment in strict accordance with the court verdict. As to the cases of serving a sentence related to isolation from society, there is a problem of unclear conditions for taking the most significant incentive measures in relation to a convicted person, such as substitution of the unserved part of the sentence and parole. The analyzed practice convincingly indicates that even if all the requirements of the law are fulfilled, petitions of convicts remain unsatisfied, while the courts refer to the fact that the goals of the punishment have not yet been achieved. Currently, in criminal and penal enforcement legislation there exist neither positive nor negative effective regulators aimed at facilitating strict and proper execution of the punishment imposed by the court.