This study was conducted to investigate levels of familiarity that librarians have with critical theory, to determine the extent to which it informs professional practices, and to examine how the social justice issues related to critical theory inform the practices of librarians who are unfamiliar with it. A survey found that librarians were versed not only in the critical theory of the Frankfurt School, but also in poststructuralism, feminism, queer theory, critical race theory, and postcolonialism. Many librarians, lacking familiarity with critical theory, were also shown to be concerned with social justice and these issues significantly affect these librarians’ professional practices. Based on these results, the authors propose the plausibility of incorporating more critical theory into library and information science programs.