The aim of this Master thesis is to describe why and how public librariesuse the social networks Facebook and Twitter. The focus is to study whatbrought about their use, how the work is carried out, ideas and objectivesbehind the use and what libraries actually convey on the networks. Themethodology is twofold: semi-structured interviews with responsiblepersonnel at four Swedish public libraries, and an ethnographic contentanalysis of four months of the libraries' status updates and tweets onFacebook and Twitter. The theoretical framework consists of a model forthe roles of the public library in society, and of discourses about thepublic library in media.Results indicate that social networks are used to market, make accessibleand inform of the library's resources and services. Furthermore, networksare used to communicate/interact with followers and to inspire people toread. We also detect a tutoring trait. Libraries also view social networksas a meeting place. What libraries do on the networks can be seen as anonline interpretation of traditional library goals. All four spaces from themodel for the new library – Inspiration, Learning, Meeting andPerformative – were represented in the objectives expressed in theinterviews. In what is conveyed on the networks focus lay on Inspirationand Meeting. Social networks also act as a place to market the physicallibrary. From a discourse perspective the study suggests that librariesexpress disidentification and demonstrate ability to remain open both todifferent media formats and different methods for library servicesdelivery. / Program: Bibliotekarie