Abstract: For more than four decades, Mary Niles Maack was a leading educator and scholar in the library and information science profession. Widely recognized for her research on gender issues and library history, often from an international perspective, Maack authored more than forty publications that focused on the professionalization of women in librarianship and international and comparative studies. In appreciation of her life's work, this intellectual biography traces the strands of Maack's thoughts and their place within her multifaceted body of work.