Theodore Deodatus Nathaniel Besterman (22 November 1904 – 10 November 1976) was a psychical researcher, bibliographer, biographer, and translator. In 1945 he became the first editor of the Journal of Documentation. From the 1950s he devoted himself to studies of the works of Voltaire.
In 1925 he was elected chairman of the British Federation of Youth Movements. Between 1927 and 1935 he was the investigating officer for the Society for Psychical Research. His first publication was a 1924 bibliography of Annie Besant; many works of psychical research followed. He was a critical researcher; in 1930 his criticism of Modern Psychic Mysteries, Millesimo Castle, Italy, a book on an Italian medium by Gwendolyn Kelley Hack, caused Arthur Conan Doyle to resign from the society. Doyle stated "... [The work of the Society] is an evil influence—is anti-spiritualist."
In the 1930s Besterman lectured at the London School of Librarianship, and edited and published many works of, and about, bibliography.
In the 1950s Besterman began to concentrate on collecting, translating and publishing the writings of Voltaire, including much previously unpublished correspondence. This was to occupy him for the rest of his life. He lived at Voltaire's house in Geneva, where he founded the Institut et Musée Voltaire and published 107 volumes of Voltaire's letters and a series of books entitled "Studies on Voltaire and the Eighteenth Century". The Forum for Modern Language Studies called Besterman's edition of the correspondence "the greatest single piece of Voltairian scholarship for over a century.".
During the final years of his life, Besterman opened discussions with the University of Oxford. These culminated in his naming the university his residuary legatee and arranging for the posthumous transfer of his extensive collection of books and manuscripts, which included many collective editions, to an elegant room in the Taylor Institution (the university centre for modern languages), which has space for 9000 volumes. This was renamed the Voltaire Room. Following Besterman’s death on 10 November 1976, the Voltaire Foundation was vested permanently in the University of Oxford. 
Besterman in 1969 published a detailed biography of Voltaire (541 pages + back matter), including many of Besterman's own translations of Voltaire's verse and correspondence.
- The Divining Rod: An Experimental and Psychological Investigation, 1926
- Mind of Annie Besant, 1927
- Some Modern Mediums, 1930
- Mrs. Annie Besant, a modern prophet, 1934
- Men against women; a study of sexual relations, 1934
- The Beginnings of Systematic Bibliography, 1935
- Water Divining,1938
- A World Bibliography of Bibliographies, 1939
- The love letters of Voltaire to his niece, 1958 (editor and translator)
- Voltaire's Correspondence 1953–65, 107 vols
- Philosophical dictionary, 1972 (translator)
- Crystal Gazing: A study in the History, Distribution and Practice of Scrying, 1965
- Voltaire, 1969
- Barber, Giles (2004). Besterman, Theodore Deodatus Nathaniel (1904–1976). Dictionary of National Biography. Oxford University Press. Retrieved 2009-11-28.
- "Science: Houdini, Doyle". Online archive (Time magazine). 1930-03-31. Retrieved 29 November 2009.After reviewing the performance of the medium. Besterman concluded: "To put forward such a book as this as a serious contribution to psychical research . . . with such claims of infallibility ... is to bring our subject into contempt and disrepute."
- Ayer, Alfred J (1986). "1". Voltaire. Weidenfeld and Nicolson. p. 19. ISBN 0-297-78880-9. "For some time Voltaire had been writing affectionately to his elder niece, Madame Denis, and from his letters – tracked down, translated and published by the indefatigable Mr. Besterman ..."
- "The present state of Voltaire studies". Forum for Modern Language Studies. Fmls.oxfordjournals.org. 1965. doi:10.1093/fmls/I.3.230. Retrieved 2009-08-03.
- Mason, Haydn. "A history of the Voltaire Foundation". Retrieved 30 November 2012.