Siyali Ramamrita Ranganathan (S.R.R.) ( listen (help·info) Tamil: சீர்காழி இராமாமிருதம் ரங்கநாதன்; 12 August 1892 – 27 September 1972) was a mathematician and librarian from India. His most notable contributions to the field were his five laws of library science and the development of the first major faceted classification system, the colon classification. He is considered to be the father of library science, documentation, and information science in India and is widely known throughout the rest of the world for his fundamental thinking in the field. His birthday is observed every year as the National Library Day in India.
He was a university librarian and professor of library science at Banaras Hindu University (1945–47) and professor of library science at the University of Delhi (1947–55). The last appointment made him director of the first Indian school of librarianship to offer higher degrees. He was president of the Indian Library Association from 1944 to 1953. In 1957 he was elected an honorary member of the International Federation for Information and Documentation (FID) and was made a vice-president for life of the Library Association of Great Britain