PURPOSE : To serve their clients in a time of post-truth discourse and fake news, librarians need to understand the post-truth phenomenon. The purpose of this paper is to examine it, what is being done in response to it, and specifically what libraries can do. DESIGN/METHODOLOGY/APPRAOCH : Recent literature on the post-truth phenomenon was examined. Traditional assumptions about the role of libraries in promoting democracy were questioned and an alternative view was put forward. Libraries’ responses to the post-truth phenomenon were examined and critically discussed. FINDINGS : Traditional assumptions about the role of libraries and information and democracy are outdated. The susceptibility of people to false beliefs and the persistence of these beliefs in spite of corrective information, is the product of many factors, including the evolving media ecosystem and psychosocial processes which are the subject of ongoing empirical research. It not primarily an information or knowledge deficit, hence there are no simple antidotes to fake news. Libraries need to rethink their responses. RESEARCH LIMITATIONS/IMPLICATIONS : The paper deals with very recent developments and relies heavily on informal online resources. PRACTICAL IMPLICATIONS : Relevant library activities are examined and suggestions are made for developing appropriate library responses. ORIGINALITY/VALUE : At the time of writing this was the first attempt in the library management literature to engage in a systematic and thoughtful manner with the literature on the post-truth phenomenon.