The purpose of this thesis is to investigate the function of the museum library. The method used consisted partly of literary studies, and partly of field investigations, conducted mainly in the form of interviews. Two different sets of field studies have been conducted. The first one is an investigation of the museum libraries in Goteborg. After a preliminary study, three of these have been selected for further investigation. These are the libraries of Göteborgs Konstmuseum, Göteborgs Stadsmuseum and Röhsska museet. Five employees from each museum have been interviewed, and asked to give their opinions of the library and its function, and also to describe how they used it. To broaden the perspective of the essay, an additional field study was made. In this, the libraries of Byggnadsvård Nääs, Stockholms Stadsmuseum and Skara Länsmuseum were investigated. All these libraries exhibit a slightly different function than the others, mostly in giving greater attention to the public part of their work. The thesis concludes that museum libraries can have served different functions, but the fundamental one must always be to provide information services for the museum itself. The library is a tool for the museum personnel, and their access to the information must be the topmost priority of every museum library. Once this is seen to, however, the library can have several other functions. Museum libraries are a source of information for researchers. It can become a way for the museum to open up its collections to the museum visitor. Pictures and archival material can be computerized and made accessible through the museum library. The library can also be a way for the museum to market itself, by attracting visitors to the museum. In addition to this, the library can be an arena for other activities to take place in, a gateway between the museum and the visitor.