APA (7th ed.) Citation

Doyle, A. P. (2011). Leo XIII., the Great Leader. Project Gutenberg.

Chicago Style (17th ed.) Citation

Doyle, A. P. Leo XIII., the Great Leader. Project Gutenberg, 2011.

MLA (9th ed.) Citation

Doyle, A. P. Leo XIII., the Great Leader. Project Gutenberg, 2011.

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