If you are citing descriptive copy or a quotation printed on the cover of a book, it’s preferable to incorporate the necessary details (chiefly, the author of the copy or quotation you are citing, if known, and the source where the copy or quotation appears) into the body of your text and then create a standard entry for the book in your works-cited list:

On the cover, the publisher calls Viet Thanh Nguyen’s The Sympathizer “a sweeping epic of love and betrayal.”

Maxine Hong Kingston, in an endorsement on the back cover of Viet Thanh Nguyen’s The Sympathizer, calls the novel “[a] magnificent feat of storytelling. A novel of literary, historical, and political importance.”

Work Cited

Nguyen, Viet Thanh. The Sympathizer. Grove Press, 2015.

If you do not include all the necessary details in the body of your text, the in-text citations and works-cited-list entries might appear as follows:

The publisher calls Viet Thanh Nguyen’s The Sympathizer “a sweeping epic of love and betrayal” (Cover copy).

Work Cited

Cover copy. The Sympathizer, by Viet Thanh Nguyen, Grove Press, 2015.

Viet Thanh Nguyen’s The Sympathizer has been called “[a] magnificent feat of storytelling. A novel of literary, historical, and political importance” (Kingston).

Work Cited

Kingston, Maxine Hong. Cover endorsement. The Sympathizer, by Viet Thanh Nguyen, Grove Press, 2015.

If the quotation is from a review of the work, you should ideally obtain the review and cite the publication in which it appeared in your works-cited list, but if you need to cite it from the book cover, your entry might read as follows:

Caputo, Philip. Review excerpt on book cover. The Sympathizer, by Viet Thanh Nguyen, Grove Press, 2015.