APA (7th ed.) Citation

Twain, M., Bruce, R. G., & Hill, H. L. (1997). A tramp abroad. Penguin Books.

Chicago Style (17th ed.) Citation

Twain, Mark, Robert Gray Bruce, and Hamlin Lewis Hill. A Tramp Abroad. New York, N.Y., U.S.A.: Penguin Books, 1997.

MLA (9th ed.) Citation

Twain, Mark, et al. A Tramp Abroad. Penguin Books, 1997.