APA (7th ed.) Citation

Keller, H. (2010). Optimism: An Essay. Project Gutenberg.

Chicago Style (17th ed.) Citation

Keller, Helen. Optimism: An Essay. Project Gutenberg, 2010.

MLA (9th ed.) Citation

Keller, Helen. Optimism: An Essay. Project Gutenberg, 2010.

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