The improper renewal of criminal proceedings is an irregular legal remedy which offers a possibility for challenging the decisions which have become final, under legally defined conditions. The improper renewal is a complex institute because theory, legislator, and even case law, have not agreed on the important issues within this institute. Generally speaking, for the topic to be better systematized, it is necessary to study the topic more, to write high quality and precise work, and compose legal provisions regulating the issue in a better way. If that were the case, maybe the institute would be more in the service of protecting the rights of the parties of the criminal proceedings. This paper deals with the criminal proceedings in general so that we can use logical sequence to come to the study of the improper renewal of criminal proceedings, because without the basic concepts and theories we can not understand the essence and meaning of more specific and complicated institutes. It starts from the basic principles, across subjects and course of action, to remedies – regular, as well as irregular. Although the proper and improper renewal are two seperate institutes, we can not explain one without touching the other. Consequently, the paper studies the differences between the proper and improper renewal, the validity, as a key insitute that is important for clarification of the subject matter, furthermore, a short overview of the historical developement of the renewal of criminal proceedings is presented, and finally we come to a concrete and systematic processing of the proper and improper renewal, guided mainly by the Criminal Procedure Act. At the very end, it is important to show a few examples of case law, in order to present the way that the proper and improper renewal of criminal proceedings look like in practice of the Croatian Supreme Court.