This thesis analyzes the action by stages in Croatian civil procedure, which was introduced by the Amendments to the Civil Procedure Act of 2003. The action by stages allows the plaintiff to file a claim in multiple stages, beginning with a request for necessary information or documentation, followed by specification of the main claim on the basis of the collected data. The thesis explores the legal nature of the action by stages, its application in practice, and compares it with the German legal system, where such action (Stufenklage) is also regulated. Particular emphasis is placed on the challenges in interpreting and applying the action by stages in Croatian court practice, especially in areas such as labor disputes and disputes regarding the nullity of contract provisions in loan agreements. The thesis also highlights the importance of this institute in protecting consumer rights, as evidenced in the case of loans linked to the Swiss franc (CHF loans), where the action by stages enabled plaintiffs to effectively realize their rights. In its conclusions, the thesis points out the need for further harmonization of court practice and a more precise definition of certain aspects of the action by stages to ensure its consistent and fair application in practice.