A great book cover can do many things: alert the reader to the quality, style and tone of the words they are about to read, say something of the author’s taste (or tastelessness), and perhaps something of the reader’s good (or bad) judgement.
The artwork on the jacket can communicate a lot about what we are about to read. In the 1940s, Mr Alvin Lustig created book covers for Messrs Federico García Lorca, Henry Miller and Tennessee Williams that took their cue from modern art, not commercial imperative. Arguably art in their own right, the covers also said something meaningful about the work inside.
Sometimes, book covers do the opposite, such as Mr Paul Bacon’s legendary design for Mr Philip Roth’s Portnoy’s Complaint. A book about masturbation, Mr Bacon wisely decided to illustrate simply with author and book name against a vibrant yellow background.