Abstract Genre separation has been common for childrens and youth fiction in Swedish public libraries, but genrefication for adults is still under lively discussion. Fantasy literature is a good example of fiction that has actually been separated for children, young people and adults for about 30 years. It therefore serves as a good example in a study about fictional genre separations. The aim of this study is to investigate how librarians determine the genre of fantasy books, how they organize fantasy sections in libraries and how they argue about genre separation and subgenres of fantasy literature. The method used in this study is qualitative interviews with six librarians with responsibility for fantasy sections at six different large and medium-sized public libraries in Sweden. Gabriel Naudés ideas of how to arrange books in a library was used as a theoretical framework to analyse the empirical material. The results of this study show that there are a variety of ways to organize a fantasy section in a public library. It shows that genre separation for fantasy literature is still developing in the public libraries surveyed. It also shows that fantasy literature in its classical form is relatively easy to genrefy, while subgenres are a little bit more difficult. In addition, it appears that the argumentation about genre separations shows a mostly positive attitude towards these, and that these separations are a good tool for readers to find books. Finally, it shows that the user-friendly perspective is strong in the libraries surveyed, and that well-thought-out fantasy sections and genre separations increase interest in the literature that is highlighted.