APA (7th ed.) Citation

Twain, M. Mark Twain's letters. Univ. of Calif. Press.

Chicago Style (17th ed.) Citation

Twain, Mark. Mark Twain's Letters. Berkeley, Calif: Univ. of Calif. Press.

MLA (9th ed.) Citation

Twain, Mark. Mark Twain's Letters. Univ. of Calif. Press.

Warning: These citations may not always be 100% accurate.