APA (7th ed.) Citation

Twain, M. (2004). What Is Man? and Other Essays. Project Gutenberg.

Chicago Style (17th ed.) Citation

Twain, Mark. What Is Man? and Other Essays. Project Gutenberg, 2004.

MLA (9th ed.) Citation

Twain, Mark. What Is Man? and Other Essays. Project Gutenberg, 2004.

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