This thesis is about medical libraries that, foremost, serve the healthcare personnel in their evidence-based practices. The visibility aspect of these types of libraries is explored, both through a librarian’s and a user’s perspective. A theory of invisible information work is applied to understand why and how visibility affects the libraries and the librarians’ work. The visibility is also explored through a user perspective, where theories of user barriers are applied to a group of users with remote access to the medical library. The data is derived from semi-structured interviews with medical librarians, clinical librarians, and a group of healthcare personnel, and analyzed thematically through the theoretical perspectives. Furthermore, the medical library as a place is explored and discussed, which deepens the analysis and understanding of the medical libraries’ impact on the healthcare personnel and their evidence-based practices, as well as the visibility and role of the medical library. The conclusion is that the library and its services, to a large extent, are invisible to the user group, and several barriers to the users’ library access and use are detected and exemplified in the thesis. Another conclusion is that medical librarians have a range of strategies to counter the invisibility, but factors such as resources and being part of a healthcare organization affect the possibility of implementing these strategies.