APA (7th ed.) Citation

Yeats, W. B. (2009). The Green Helmet and Other Poems. Project Gutenberg.

Chicago Style (17th ed.) Citation

Yeats, W. B. The Green Helmet and Other Poems. Project Gutenberg, 2009.

MLA (9th ed.) Citation

Yeats, W. B. The Green Helmet and Other Poems. Project Gutenberg, 2009.

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