The aim of this master’s thesis is to create an updated image of why and how staff at public libraries in Sweden work with social media in 2019 and what challenges they experience in this work. The study is based on interviews with nine persons who are working with social media in public libraries. The results were analyzed through the theoretical framework Relationship Marketing, developed by Evert Gummesson. The result of the study shows that the primary purpose of the libraries' use of social media is to spread different types of information concerning the libraries and their activities. To communicate with the users is another purpose, but not as prominent as the information part. All libraries in the study use Facebook and all but one uses Instagram. At most of the libraries, one seems to mainly value the followers one has, while at other libraries one wants to reach new followers and attract new library visitors. Lack of time and resources, unclear strategies and the GDPR-law are the challenges that the respondents experience in the work with social media, as well as the difficulty in standing and reaching out in the information society we live in today.