The aim of this master´s thesis is to analyse what factors have an impact on the quality of school libraries. The research questions are: How do some school principals, school librarians and school inspectors view quality in school libraries and what has an impact on quality? How do they view some existing quality criteria? How important do they think the integration of the school library into the curriculum is? The theoretical approach is derived from research about school libraries by David Loertscher and by Sharon Markless and David Streatfield. The empirical material has been collected through half structured qualitative interviews. The informants chosen are principals and school librarians from three Swedish primary schools (6-15 years). The schools are chosen because their libraries have been awarded the title school library of the year. Two school inspectors have also been interviewed. Some of the aspects of quality that both the research literature and the interviews show as important factors are cooperation and collaboration between school librarians and teachers, learning by ICT and students' information literacy. The investigation shows that earlier research is valid for this thesis also. The views of the informants are that school libraries can play a vital role in schools. The investigation confirms the importance of support from principals and of evaluation of your work, by the help of school inspections and existing quality criteria.