The purpose of this master thesis is to engage in subject cataloging and indexing in libraries, with an emphasis on the principles and professional ethics applied in practice, which serves to describe and collect all library materials covering a certain area, and to enable the international exchange of bibliographic data and access to materials for users. The paper will deal with the international principles of creating subject catalogs and the emergence of subject headings, and provide insight into how the personal attitudes and dominant social values of subject experts and catalogers influence the design of subject systems and the organization of knowledge in general. Based on the available literature, the online catalogs of the Library of Congress as one of the authorities for subject cataloging, and the subject system of the National and University Library in Zagreb, the paper will offer an overview of the practice of creating subject headings with regard to certain phenomena and problems that include the interpretation of the content of a material unit, representation and the presentation of some marginalized groups. It refers, for example, to members of the LGBTIQ+ community, national and ethnic minorities, etc., issues of national identity and bias in the analysis of certain contents, and in general issues of political correctness and naming using examples from the past and comparison with the current situation. Examples of good practice will also be presented and solutions offered for recognizing and avoiding such practice.