This thesis provides an overview of the archival processing of archival and registry holdings belonging to the XV. Gymnasium which was performed as part of the student practice in the mentioned institution. The thesis comprises a theoretical framework which is expanded and developed through the creation of a comprehensive list of archival and registry holdings belonging to the XV. Gymnasium, a finding aid and a classification scheme for archival and registry holdings, that were created after determining the existing condition of the holdings, the entry of the listed holdings into NAIS (formerly known as ARHiNET) as instructed by the competent archive, the formation of multiple fonds because of the changes in the name of the creator through the years and their short description up to the level of subseries. The thesis also comments on the amendments made to the Special Regulations on the protection and processing of archival and registry holdings of The XV. Gymnasium, which were necessary for creating a list of registry holdings for disposition, the aids and resources that were used and the problems that appeared such as the change in the holdings’ names through the years.