PurposeThe purpose of this research is to comprehensively describe the legitimacy of the public library in the 21st century.Design/methodology/approachThe research involved a comprehensive literature review using the Library and Information Science Abstracts (LISA) database with keywords “Library” and “Legitimacy”, combined with citation searches and additional collections. In total, we analysed 159 research articles primarily from the 21st century, with some comparative analysis of pre-2,000 works. The final phase of the research investigated libraries’ legitimisation efforts across various dimensions, examining how they employ rhetoric and theories to maintain legitimacy amidst challenging circumstances.FindingsThrough this research process, five dimensions of public library legitimacy emerged; (1) Democracy, (2) Culture and History, (3) Communication and Education, (4) Economy and (5) Librarianship, with the most diverse literature being related to democracy, and its subsections intellectual freedom, neutrality, the public sphere, social justice and social capital.Originality/valueThe outcome of our results indicates that the evolving legitimacy of the public library in the 21st century has become multifaceted, compared to the elements of legitimacy in the 20th century. Contemporary public libraries can continue to utilise the dimensions of legitimacy identified in this study and can reconstruct their legitimacy accordingly.