Answer: Citing the Back Cover of a Book

Even though citing a book’s back cover is unusual, this is how a proper footnote could represent such a situation (this is only an example):

1 Robert Radford, Footnotes, Endnotes, Electronic References and Bibliography Methodology, Morrisville: Lulu, 2008, back cover.

It is also worth noting that you could employ the term “fourth cover” (quatrième de couverture in French) instead of “back cover”:

1 Robert Radford, Footnotes, Endnotes, Electronic References and Bibliography Methodology, Morrisville: Lulu, 2008, fourth cover.

The inside front cover of a book is called a “second cover” and the inside back cover is known as the “third cover”.