In this dissertation we analyze pseudonym procedure during catalogization according to Croatian catalog rule books. Special attention is paid to the concept of authorship and 'authors in catalog', types of authorships, attributing of the literal works and the reasons behind anonimity and pseudonymity of the author. The motivation for the dissertation is the new rule book called 'Pravilnik za opis i pristup građi u knjižnicama, arhivima i muzejima', also known as 'KAM rule book'. The goal of this dissertation is to compare the new KAM rule book to the old one which is called 'Pravilnik i priručnik za izradbu abecednih kataloga' written by Eva Verona. It is also established how pseudonyms and authors are treated in the old rule book compared to the new one. The method used in it is comparative analysis. After each of the rule books is introduced, a comparative analysis is shown in the table, followed by a brief discussion which explains each rule book's stance on pseudonyms. Expected result of this dissertation is to find out if there are any differences between those stances and, if so, determine just how significant they are.