Nook Farm: Mark Twain's Hartford Circle.
Andrews, Kenneth R.
Seattle: University of Washington Press, 1950

Mr. Clemens a Mark Twain: A Biography.
Kaplan, Justin.
New York: Simon & Schuster, 1966.

The Mark Twain Encyclopedia.
Lemaster, J. R. and James D. Wilson, ed.
New York: Garland Publishing, 1993.

Susy and Mark Twain Family Dialogues.
Salsbury, Edith, ed.
New York: Amereon House, 1965.

The Quotable Mark Twain: His Essential Aphorisms, Witticisms, & Concise Opinions
Rasmussen, R. Kent
Chicago: Contemporary Suggested Reading List, 1997.

Mark Twain A to Z.
Rasmussen, R. Kent.
New York: Oxford University Press, 1995.

Mark Twain's Letters 5 vols.
The Mark Twain Papers.
Berkeley: University of California Press, 1988.

Mark Twain's Own Autobiography: The Chapters from the North American Review.
Twain, Mark.
Madison: University of Wisconsin Press, 1990.