Brooks, Van Wyck. The Ordeal of Mark Twain. New York: E. P. Dutton, 1920.

Brooks's work is dated but still interesting, especially as an example of early Twain biographies.

Commire, Anne, ed. Something about the Author. Vol. 1. Detroit: Gale Research, 1971. Contains a biographical entry on Wood.

Etheridge, James M., ed. Contemporary Authors. Vols. 9-10. Detroit: Gale Research, 1964. Includes a biographical entry on Wood.

Geismar, Maxwell. Mark Twain: An American Prophet. Boston: Houghton Mifflin, 1970. Geismar believes that the works of Twain's final period have not had the recognition they deserve.

Lauber, John. The Making of Mark Twain. New York: American Heritage, 1985. This biography deals with Twain's apprenticeship as a writer.

Leary, Lewis. Mark Twain. Minneapolis: University of Minnesota Press, 1960.

This is a good, brief introduction to Twain's writings.