ENPurpose. This paper aims to provide an overview of library services and programs for adults in Lithuania, focusing on two prominent institutions: the Adomas Mickevičius Public Library and the National Library Martynas Mažvydas Library located in the capital Vilinus. By examining these libraries’ structures, organization, and range of services, this study sheds light on the broader landscape of library services in Lithuania. Methodology. The case analysis method has been conducted on the basis of observing the daily work of the Adomas Mickievičus National Library in Vilnius and a professional visit to the Martynas Mažvydas National Library during the authors’ professional training in the Erasmus+ program for adult education. The analysis draws on a combination of primary and secondary sources, including interviews with the library staff, the analysis of the official documents, and the existing literature on library services in Lithuania. Results. The paper will provide insight into the organizational structure of Lithuanian library services and programs for adults through the lens of two prominent institutions. It will also provide basic information about the possibilities of professional development of librarians as part of the Erasmus+ program, specifically about the method of job shadowing as a form of professional development by observing and monitoring the work of colleagues from a comparable European institution. Practical implications. The knowledge about the work of Lithuanian libraries can serve as an example for other libraries in Croatia to guide them when introducing changes and innovations in their library programs and services for adult users, to improve the quality of library services in general, and increase the satisfaction of their users.Value. The value of the study lies in spreading knowledge about Lithuanian library services and programs for adults, as well as the possibilities for the professional development of librarians through the Erasmus+ program. The findings can inspire discussions on improving and expanding library services to meet the changing needs of the communities they serve. Keywords: Adomas Mickevičius Public Library; the Erasmus+ program; job shadowing; Lithuanian library services and programs for adults; National Library Martynas Mažvydas.