The aim of this paper is to analyse some of the aspects of sustainable development in Croatian school libraries within three operational groups (direct educational activity, professional library activity, cultural and public activity) in order to improve the understanding of school librarianship. The new challenges brought by the digital maturity of school institutions (primary and secondary schools, dormitories) and the new Global Goals of Sustainable Development by 2030 have influenced the change in the work tasks and activities of school librarians, which are based on inclusiveness, visual identity and sustainability of schools/dormitories both within and outside the existing frameworks of action. The positive and negative effects of school library operations were also affected by the Covid-19 pandemic. The research is quantitative, the method is an online questionnaire, and the data were statistically processed in the Statistical Package for the Social Sciences - SPSS. The results show that a large number of library professionals are not empowered with the new professional skills of sustainable development, that they cooperate with colleagues from the school regarding the implementation of activities on sustainable development, that printed materials on environmentally friendly business operation and sustainable development are ahead of electronic and digital ones, that a smaller number of librarians are involved in projects, etc.