Today book covers straddle the divide between art and commerce. Just as great design must convey the brand essence, so cover illustrations must sell the story concealed within.
The changing role of book cover design reflects changing attitudes towards books over time. In the Middle Ages tomes were encrusted in jewels and dusted in gold leaf, a testament to their value. With the proliferation of libraries in the Georgian period books were widely available yet reading was regarded as a rather sober affair, reflected in the era’s restrained leather-bound volumes. The modern dust cover, with vibrant illustrations and bold typefaces, owes its origins to the United States, where in the 1920s the rise of mass communications and increase in consumption encouraged publishers on both sides of the Atlantic to introduce richer visuals to entice passers by to purchase.
Penguin was one of the first to enter the fray. Instigated by Allen Lane and later refined under Jan Tschichold, the paperbacks marry a clear logo with a classic yet contemporary typeface and a colour coded three-band cover to create a range that has stood the test of time. 
In the twenty-first century publishers are multi-national conglomerates and books must compete against a host of other forms of entertainment in crowded supermarket aisles. As a result some feel that book illustration has become formulaic and thoughtless, a case of shrewd picture editing rather than ingenious design.
However if you look hard enough it’s still possible to find exceptional cover designs that sell their wares without prostituting themselves.
Ebooks may be convenient but they simply can’t compete with beautiful, tactile book covers. Coralie Bickford-Smith’s designs for Penguin Classics are a case in point. Here she has managed to capture the essence of Fitzgerald, immediately transporting the prospective buyer to the louche glamour of 1920s New York.
In a crowded marketplace minimalism and attention to typography make a book stand out.
The unexpected also helps to get you noticed. By opting for monochrome in a category awash with involving food photography Caz Hidebrand’s cookbook draws attention to the craftsmanship in every piece of pasta.
So ignore the old expression - make sure you do judge a book by its cover. After all that’s exactly how your brand is going to be judged.
Following on from this post we'll be featuring some more of Bloom's favorite book covers on the right hand side of the blog. This week’s suggestions came courtesy of Jenny Dean. Let us know your favorites and keep an eye out for new additions.